Where does Calmet write when idolatry began? I saw someone mention that Calmet writes that idolatry was started by Ham or his son Canaan. Where can I find this passage in Calmet's writings?
Dictionnaire historique ... de la Bible

Usually when someone cites Calmet, it is a reference to his 1722 Dictionnaire historique, critique, chronologique, géographique et littéral de la Bible, published under the English title Dictionary of the Holy Bible.  I will use this English translation for my answer.  It has some additions by an American author, but these are clearly marked in the text, so it remains clear what Calmet wrote originally.

In the entry for Ham, no mention of idolatry is made.   The entry for idol says:


  Writers are not agreed about the origin of idolatry, or the superstitious worship paid to idols and false gods.


However, I did find a couple of mentions in other places.  The entry for Nimrod says:


  To Nimrod is imputed the invention of idolatrous worship paid to men.


And the entry for Teraphim in the expanded edition says:


  Father Kircher, Oedip. AEgypt Synt. iv. eap. s. and after him Ceneus, in his Republic of the Hebrews, maintain that all idolatry came from Egypt; and that the use of teraphim passed from that country into the east; for that Ham, or his son Mizraim, were the inventors of statues.


Assuming that the person mentioned by the OP got the information directly from Calmet, it was probably this passage.  It doesn't actually express Calmet's opinion, though, but could easily be misread to do so (i.e. thinking only the first line of the paragraph comes from Kircher/Ceneus.)

Commentaire littéral sur tous les livres

I also checked Calmet's other major work, Commentaire littéral sur tous les livres de l'Ancien et du Nouveau Testament.  The volume on Genesis mentions idolatry a number of times, but not in connection with Ham as far as I can tell.  In commentary on chapter 4, he writes:


  On commença alors profaner le nom du Seigneur, en le donnant aux Idoles. C'est la tradition de plusieurs Juifs, que l'idolâtrie commença s'introduire dans le monde sous Enos. 
  
  We then began to profane the Lord's name, giving it the Idols. It is the tradition of many Jews, that idolatry began to break into the world under Enos.


In commentary on chapter 11, he writes:


  Epiphane met l'origine de l'idolâtrie sous Sarug. Les premières idoles ne furent, dit-il, que de simples peintures. Tharé pere d'Abraham introduisit l'usage des statues des figures de métal, de bois de pierres. L'Ecriture nous apprend que Tharé adoré les
  idoles, comme nous le montrerons ci-aprés mais on n'a aucune preuve certaine que ni lui ni Sarug ayent inventé cette pernicieuse coutume. 
  
  Epiphanes puts the origin of idolatry under Serag. The first idols were not, he said, than just paintings. Terah, father of Abraham introduced the use of figurines of metal, wooden, and stones. The Scripture tells us that Terah worshiped idols, as we show here after but we have no certain proof that neither he nor Sarug invented that pernicious custom.


And in commentary on chapter 15, he says:


  il est certain que la plupart de ses ayeux étant morts dans l'idolâtrie font privez du bonheur éternel
  
  it is certain that most of his [Abraham's] forefathers having died in idolatry are deprived of eternal happiness.


In his commentary on the Book of Wisdom, Calmet has a long essay on the origin of idolatry.  The key paragraph starts:


  Quelques Pères ont cru que Sarug ayeul de Tharé et le septième depuis Noé avoit inventé l'idolâtrie depuis le déluge. Mais on ne trouve aucune preuve de ce sentiment. L'Ecriture dit d'une maniéré assez distincte que Tharé, pere d'Abraham, que Nachor ont été d'abord engagez dans le culte des Idoles; elle insinue la même chose en parlant d'Abraham; ce qui fait juger que ce culte impie n'étoit que trop ancien dans le monde puisqu'il étoit déja si répandu.
  
  Some Fathers have believed Serag, grandfather of Terah and the seventh from Noah, had invented idolatry from the flood. But we can find no evidence of that suggestion. Scripture tells rather clearly that Terah, father of Abraham, and Nahor were the first engaged in the worship of idols; it insinuates the same thing by speaking of Abraham; which judges this impious worship was only too old in the world since it was already so widespread.


This appears to represent Calmut's view.  A bit later in the same essay, there is a paragraph on Ham:


  D'autres rapportent à Cham, fils de Noé, l'originc des Idoles; d'âutres, à Chanaan son fils. On veut que Cham soit le même que Zoroastre, si fameux parmi les Anciens, &amp; si peu connu par ceux-mêmes qui en parlent. On attribue Cham l'invention de la magie, &amp; des arts dangereux qui y ont rapport. On veut que Chanaan ait répandu la superstition, &amp; le culte des faux Dieux parmi les Phéniciens, &amp; les Cananéens ses descendans, par le moyen desquels il s'est communiqué aisément par tout le monde. Sanchoniathon nous donne une Théologie presque complette des Phéniciens; &amp; on voir par ce qu'il en dit que la fausse Religion a commencé dans ce pays, presque aussi-tôt que le monde. Mais ceux qui nous parlent de Cham, &amp; de Chanaan n'ayant point de preuves positives de ce qu'ils avancent, on ne peut faire aucun fond sur leur rapport. D'ailleurs on fait que Sanchoniathon est un auteur forgé apparemment par Porphyre &amp; qui n'exista jamais.
  
  Others relate to Ham, son of Noah, the origin of the idols; others, to his son Canaan. They want Ham to be the same as Zoroaster, so famous among the ancients, and so little known by those of whom we speak. They attribute to Ham the invention of magic and the dangerous arts that it entails. They want Canaan to have spread superstition and the cult of false gods among his descendants, the Canaanites and Phoenicians, through whom it is easily communicated to all the world. Sanchoniathon gives us an almost complete theology of the Phoenicians; we see he says the false religion began in this country, almost as early as the world. But since those who speak of Ham and of Canaan have no positive evidence for their claim, one can put no backing on their report. Moreover it is a fact that Sanchoniathon is an author apparently made up by Porphyry who never existed.


Based on the followup comments by the OP, this appears to be where the idea came from.  What Calmet is actually saying is that some scholars attribute the advent idolatry based on a passage in Porphyry's writing which itself apparently quotes someone know as "Sanchoniathon".  Porphyry (Latin Porphyrius) was a pagan philosopher and vocal opponent of Christianity in the late third century.  Calmet, however, basically calls the idea nonsense made up by Porphyry.

Summary

It appears that Calmet believed that idol worship began with Terah or possibly his father, Nahor.  It appears that the passage the OP refers to comes from Commentaire littéral sur tous les livres, but the passage is not expressing Calmet's view, but rather other scholars.  Ultimately, the idea stems from the pagan philosopher Porphyry.