Onkelos was the nephew of Emperor Hadrian, so he probably lived in Rome.

Emil Brederk has written:

'Konkordanz zum Targum Onkelos' -- subject(s): Targums

If you mean Onkelos, he is mentioned several times in the Talmud.

According to the tradition, he was a prominent Roman nobleman.

A targum is an Aramaic translation of the Hebrew Bible. There are several, but if someone says just "the Targum" they are probably referring to the Targum of Onkelos. This targum still studied regularly by Jews today. In making a translation, any translator has to interpret the text being translated, and Onkelos' translation serves as an important commentary on the Bible.

Two reasons

a) because Son of God was an AKA for the Word or Memra of YHVH (God manifest)...see the Targums Jonathan and Onkelos, and

b) because He had no human father