When is "Thanks Be to God" said in the mass? When do we say "Thanks be to God" in the mass, is it in the Liturgy of the Word? Also when do we say "Praise to You Lord Jesus Christ" in the mass, is it after the Gospel?
Since you only mention the mass and not a denomination, I'll assume you mean in the Catholic Church. However, the same will apply for most liturgical traditions

After each of the first (often Old Testament) and second ( New Testament)  lessons, the reader will say


  The word of the Lord


to which the people respond 


  Thanks be to God.


The Gospel reading is announced by


  A reading from the holy Gospel according to N. 


The people respond 


  Glory to you, Lord.


After the Gospel reading, the reader says


  The Gospel of the Lord. 


The people respond


  Praise to you, Lord Jesus Christ


At the end of the mass, the people are dismissed with (or something similar)


  Go forth, the Mass is ended


And again the people respond


  Thanks be to God