According to trinitarians, especially Protestants, who is Wisdom in Proverbs? In general, Wisdom can be (and is, and was) identified as Jesus. However, there is this verse:


  Proverbs 8:22 (NLT)
  22&nbsp;"The Lord formed me from the beginning,
    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;before he created anything else."


Hold on a moment...I thought God the Son wasn't created, having coexisted with God the Father since before time? How is the identity of Wisdom established as being that of the Son and how is Proverbs 8:22 handled? If it makes a difference, I grew up Wesleyan, so I'd prefer Protestant doctrines although Catholic or Orthodox doctrines would be interesting too.
There are two common interpretations among Protestants:

&quot;Wisdom&quot; refers to the Word of God; that is, Jesus
&quot;Wisdom&quot; is the personification of a divine attribute, and perhaps a type of Christ, but should not be understood to be Jesus himself

The first view was widely held by the church fathers and several centuries of Protestants.  However, in the 20th century the second view became more popular and now dominates Evangelical scholarship.
The Word of God: Jesus
The typical patristic understanding of this passage was that Wisdom refers to the Word of God: that is, the Son of God, Jesus.  As you note, this raises some questions about the meaning of one key word in verse 22, translated &quot;created,&quot; &quot;formed,&quot; or &quot;possessed,&quot; and this verse was a major battleground in the Arian controversy.
Early Protestants generally followed the patristic understanding, and argue that Jesus's divinity should not be doubted on the basis of this passage.  I'll provide a sampling of arguments, but to be clear, the vast majority of early Protestant commentators (particularly prior to the 20th century) take this approach.1
Matthew Henry summarizes this position, noting the very personal characteristics of Wisdom:

That it is an intelligent and divine person that here speaks seems very plain, and that it is not meant of a mere essential property of the divine nature, for Wisdom here has personal properties and actions and that intelligent divine person can be no other than the Son of God himself.2

Defenders of this view point to New Testament passages referring to Jesus in similar ways, such as John 1:1, Hebrews 1:3, 1 Peter 1:20 and Colossians 1:15–18.
But if that's the case, how do Protestants defend against the Arians and others who say that this passage teaches that Jesus was created?  The question revolves around the meaning of the Hebrew word qanah, which elsewhere in the Old Testament can be translated &quot;get,&quot; &quot;acquire,&quot; &quot;create,&quot; and &quot;possess.&quot;  Protestants argue for the &quot;possess&quot; translation, and note that the &quot;create&quot; reading would imply that at one point God was without wisdom:

Not &quot;created me,&quot; as the Targum and the Septuagint. [...] [T]his possession [...] denotes the Lord's having, possessing, and enjoying his word and wisdom as his own proper Son.3

Albert Barnes similarly says that there is no &quot;ground for the thought of creation either in the meaning of the root, or in the general usage of the word.&quot;  His Notes go on to point out the logical difficulty of &quot;create&quot;:

What is meant in this passage is that we cannot think of God as ever having been without Wisdom.4

The Personification of a Divine Attribute
The Moody Bible Commentary, citing several recent commentators,5 provides a helpful summary of the alternate position:

Lady Wisdom here is no more than a personification of the wisdom that the sage has received, a wisdom revealed by God and rooted in His very own character.  The context simply does not justify interpretations that go beyond the personification of wisdom here. [...] It is therefore best to say that Lady Wisdom shares similarities with Christ, but Christ is even greater than she.  In short, the sage's wisdom is a type of Christ.

Others understand the text similarly.6  The Reformation Study Bible, though emphasizing Christ as the wisdom of God, still considers the personification of wisdom here to be a &quot;poetic device&quot;:

Although it is premature to see personified wisdom (especially in vv. 22–31) as a direct portrayal of a divine being, there is no doubt that the revelation of Jesus Christ as the wisdom of God shows us the significance of a wisdom that is its own absolute authority.

This view was not entirely foreign to writers of the 19th century.  Methodist Adam Clarke (1760–1832) critiques the church fathers as finding &quot;allegorical meanings every where,&quot; though he too applies Wisdom in verse 3, &quot;She crieth at the gates,&quot; to Christ, his apostles, and their successors.7
Summary
Each person's understanding of this passage will be influenced by the relative weights placed on the testimony of the church fathers and modern hermeneutics.  Early Protestants leaned toward the former, but the latter has gained primacy among Protestants over the last two centuries.  Either way, however, Protestants have carefully argued that the text does not challenge the divinity of Christ.

References:

Geneva Study Bible, Wesley, Coke, Poole, Scofield.  Also Catholic Haydock.
Henry, Commentary on the Whole Bible, III
Gill, Exposition of the Whole Bible.  Cf. James Coffman; though not a defender of this view, he writes at length on how to properly translate this word.
Barnes, Notes
Kidner (Proverbs), Longman (Proverbs), and Waltke (Book of Proverbs 1-15), among others.
ESV Study Bible, NIV Study Bible, and Keil &amp; Delitzsch, for example.
Clarke, Commentary