What's you up to?

[Glizdka]

Unlike "How's things?" and "There's a lot of people here", I suspect "How's you doing?" and "What's you up to?" not to work.

Please confirm.

 

[Rover_KE]

Confirmed.

 

[Glizdka]

Is it because 's can (sometimes) work with plural nouns, but not pronouns?

How's your finals going? :tick:
How's you doing? :cross:

 

[Charlie Bernstein]

Is it because 's can (sometimes) work with plural nouns, but not pronouns?

How's your finals going? :tick:

That's a little strange to my little ears, but maybe someone would say it.

How's you doing? :cross:

Never. In casual American English, we say "How you doing?" (pronounced "How ya doin'?")

The exact pronunciation depends on the region, but you get the idea.