I was just trying to formulate a sentence in an email, and wanted to reference a third person, inquiring as to which of something that person was referring in the forwarded mail message.

Is it:

"About which things is he talking?"

or

"About which things are he talking?"

Just FYI I originally had the "about" at the end. Not grammatically correct but no one talks like that anyway.

There seem to be conflicting rules here, but I don't know which one applies. Normally, with sentences like "What is he doing?" the "is" is part of "is talking," and similarly the second person "are talking." This would indicate that the first version is correct. But you could also argue that the helper verb applies to "things", and so should be "are" because "things" is plural.

I started to think that "is he" is correct, because if you turn the sentence around to answer it, you get "He is talking about those things" and not "he are talking". But still, there are other sentences like "Which gifts is he bringing to the party?" Now that just feels wrong, saying "gifts is" like that. But is it correct?