The person who found this page because they did a keyword search for “Snodgrass gospel Thomas” is almost certainly looking for:
Snodgrass, Klyne. “The Gospel of Thomas: a Secondary Gospel.” Second Century: A Journal of Early Christian Studies 7, no. 1 (1989-1990): 19-38.
No idea where you might find it electronically, mind you, but it’s the only thing I’m aware of that Snodgrass has written on the Gospel of Thomas, although he does mention Gos Thom in his new book on parables whenever it’s relevant.