John 14:14, Acts 20:28, 1 Tim 3:16, 1 John 5:7, and certain others have textual problems that prevent them from being Trinitarian proof texts. Most are certainly textual corruptions, and the rest have too many ancient alternate readings to be certain one way or the other.
Matt 28:19 - mentions three names, does not say they're one being. Very ambiguous.
John 1:1 - many Greek scholars say there are three possible meanings: indefinite, definite, qualitative. Acts 28:4 says "This man is *a* murderer" in most (if not all) English translations. The syntax matches John 1:1. Therefore, John 1:1 is ambiguous and not clear.
John 8:58 - some Trinitarian scholars and translations view this as Present tense extention from the past - "I have been existing since before Abraham was born." If "I am" is a name and not the subject and verb of the sentence, then by definition it is ambiguous. The same syntax is found in John 15:27, and in most English Trinitarian translations it is rendered in the English Perfect, like the NWT's John 8:58. This verse is ambiguous.
John 10:30 matches John 17:21 and 1 Cor 3:8, with "one" in the neuter gender in the Greek. The disciples were not one being. Paul and Apollos weren't one being. Jesus and the Father are not one being. James 2:19 and Mark 12:29 say that God is "one" - one being. This is in the masculine gender in the Greek. I would say this verse is *not* ambiguous (in the Greek, it is ambiguous in English translations) - it clearly denotes one in purpose, one in unity, and not one being.
John 20:28 lacks a verb, hence it is by definition ambiguous. The NET's footnote implicitly admits this:
"Should Thomas' exclamation be understood as two subjects with the rest of the sentence omitted ("My Lord and my God has truly risen from the dead"), as predicate nominatives ("You are my Lord and my God"), or as vocatives ("My Lord and my God!")? "
Of course, the NET only offers Trinitarian interpretations. But the point is, it lacks a verb, and is thus ambiguous. If it is in the Nominative of Exclamation (GGBB, Wallace, pgs. 59-60) - it fits the requirements - then it *cannot* be direct address, aimed at Jesus. There are too many options, it is ambiguous.
Romans 9:5 lacks a verb, and is thus ambiguous. Footnotes in many Bible translations alert the reader to valid, alternative interpretations - because it is ambiguous.
Titus 2:13; 2 Peter 1:1 - some appeal to the "Sharp Rule," but this has been called into question by many. Although many insist this "rule" has been proven beyond a doubt, many translations made by competent Greek scholars still alert the reader that there are two ways to translate this verse. Those who insist on this rule have to explain away the many exceptions to the rule found in Koine Greek extra-biblical literature. Also, the Sahidic Coptic version made during the Koine Greek era sees Titus 2:13 as "God *with* our Saviour Jesus Christ." Also problematic is that "Saviour" may have been functioning as a proper name in the Greek, and the "Sharp rule" doesn't work with proper names. 2 Peter 1:1 has textual variants. Both verses are thus ambiguous.
You are right, there are no clear, unambiguous Trinitarian "proof texts."
Colossians 2:9 - the Greek word is, according to Friberg: θεότης, ητος, ἡ as an abstract noun for θεός (god); divinity, deity, Godhead, divine nature.
As an abstract noun, this is not speaking of identity, but quality. "Godhead" is possibility, but so is "divinity" and "divine nature." JWs agree that Jesus was divine, and that he reflected God's divinity.
Hebrews 1:8 - There are three possible translations. This verse also lacks a verb, hence it is ambiguous. Some translations render it as "Your throne is God," or something similar. Some translations render Ps 45:6 (of which Heb 1:8 is a quote) as "Your throne is God," or something similar.