To indicate the difference between being skilled and not skilled, use po' and tlhIb.

A "professional," meaning someone who does something because it's their occupation (as opposed to hobby) or official position is a 'ovjeq'IS. Often the slang term yaS (literally "officer") is used.

An "amateur," someone who does something but does not consider this activity to be their occupation or something done as a part of their official duties, is a Sutlhne'. There's also a slang term, tavwI', based on the expression tav neH "tinker" (verb). 

A 'ovjeq'IS may or may not be po'; likewise, a Sutlhne' may or may not be tlhIb.