Learn English – Is “too” not only an adverb, but an adjective as well

I had a discussion about this recently. We all agreed that Yes and No were minor sentences when used this way. We also hit Wikipedia trying to decide - plus we're not linguists, so its not like our decision was authoritative. But here's our reasoning:

Definition: "A Minor Sentence is one that does not necessarily have a main verb in it, but which can be understood as a complete unit of meaning." When used as you do in your examples, the minor sentence becomes part of a compound sentence.

We went back and forth on a few of the listed other choices, and decided that adverbs were out since Yes isn't modifying the verb directly, and interjections were only valid if the Yes or No was used as a response such as:
Person A: "I've just secured us two tickets to the basketball game tonight."
Person B: "Yes!" (indicating excitement).

As to why opinions are divided, well... English is a bit of an anarchical language. It seems to be human nature that unless there's an established set or rules or an authority to base your arguments on it's hard to convince people to come to agreement.

"When" is an adverb of time, referring to the verb "see" - In other words, modifies it.

In your example, it's an interrogative adverb, meaning "at what time".