Can you have 2 or more wage granishment at one time? And can they garnish with out being served?

Yes, in some cases you can have concurrently running garnishments. Generally the first one will take the max until paid, but sometimes they may be split.

Served by whom. Once they obtain a judgment, they only have to server your employer, not you.

To do a garnishment they have to normally have a judgement ( except for some student loans) but after they have a judgement, their is no additional notice you will receive normally.

A few states ( TN is one of them) that requires you to be given a notice, but there is no penality for not, so no one normally does, they stll get a garnishment, and nothing is done about no notice