This looks like fun! I have a website devoted to diagramming sentences. It's called English Grammar Revolution.
So, I thought I would be the perfect person to help you out!
1) "The two sculptors I have studied are he and Alexander Caulder."
Yes, he is correct. It comes after the linking verb are, and it is acting as the predicate noun.
I have studied is an adjective clause modifying sculptors. It has a missing - or implied- relative pronoun (that).
2) "The sundial, or sun clock, is one of the oldest type of clock."
sun clock is acting as an appositive renaming sundial. I'm not really sure about the or.
It could be older or oldest depending on what you want to say. But, both of them should use the words "types" and "clocks."
I attached photos of both of the sentences diagrammed.
I hope that helps!