Is it enjoyable or painful if somone sucks hard on clitoris or labia?

It's definitely possible to suck too hard, but I wouldn't worry about it. As long as you progress gradually, the girl should have no trouble telling you what's too much.

Same goes for fingering. I cannot stand finger friction and jamming a finger in and out like you are trying to unplug a clogged drain. Either way, think soft and gentle and suck it like you are kissing her with passion! WEEEE!

yes, there is a point where it becomes really painful.
but a little sucking never hurt anyone.

It can be painful so be gentle, and watch out for teeth! The clitoris alone is even more sensitive than the penis so don't do anything to her that you wouldn't want on yourself. Also pressure is more enjoyable than sucking for girls so make good use of your tongue.

Yes, it is possible, and can definitely be painful, mainly on the clit. Start out soft, and tell your woman to let you know when to stop increasing pressure.

Gentle sucking is wonderful, sucking too hard will likely end the session (it takes some work to make it painful but it is possible).