How do you tip at a Dim Sum place?
Do you mean how much or do you really mean "how"?
I usually do a 15% if you are asking how much
How? I tip it at the cashier, but often I leave the tip (in cash) at the table partially under the teapot. You can go up to the waiter or waitress and hand the tip to him/her directly if you want, but that is a bit unusual and I think I only did that when I were a kid (when parents send little kids out to do their dirty works)
(*Edit* I either pay my tip along with my entire bill at the cashier or I leave the tip (cash) on the dining table. I don't mean both.)
Keep in mind, that tips are usually shared in a busy Chinese dim sum place because a Chinese dim sum restaurant does not function like a typical Western restaurant. You don't have a dedicated server, so it won't make sense to have one server to pocket the entire tip.
I assume you are figuring in the cart ladies who sell, serve and service tables, plus the servers who remove dishes, bring water and requested condiments. There are many more people servicing customers than at other restaurants when you think about it. I assume they all share in the tips, so I leave the same as I would at any other restaurant; meaning about 20%.