How do I raise friendship with Whis

[bumbum]

I know it goes up after talking to him, but I dunno what I do to trigger it

[Sepulchure]

Do PQs with him accompanying you (be sure to talk to him after every quest) or have him as your active Instructor and do the What-if DLC Storyline to max it in one go after completion.

[ChaosBahamut]

iirc using techniques you learn from him also helps raise the friendship meter a bit.