Identify the Subject
He brought out some paper and a pen and inkpot.
He
I began to ask him if he had met his older self, but then I bit back my words.
There are two; this sentence is composed of two independent clauses joined by a FANBOYS conjunction. "I" is the subject on both sides.
They've created an engine that favors asocial behavior and obsessive personalities.
They
No one is in his office except the librarian.
One
Glancing around, Viv decided that she was extremely proud of the shop's interior.
Viv