I have a client which or that requires .....
What should we put here .. Which or that.....
I have a client which or that requires .....
What should we put here .. Which or that.....
Bhai's choice is the best, but "that" would also work for an individual.
Well, I agree it's not uncommon, but I don't think it's "teachably correct." (ugh)
And completely acceptable in BrE, at least in informal conversation.But it is very common.