I have a db, that I used to maintain as a end user, now it's in a multiuser environment, problem is the user has to enter job numbers.
Below are all valid job numbers, therefore a mask will not work.
So I was thinking "HOW" could this be done, perhaps eliminating Spaces, underlines and dashes from this field. How would I do this on the same field for all 3 conditions (course i would have to backtrack)

01-AB134
02-091
2-2177
3-715
03-021-A
05-001-PBPL
07-07-955

Are you saying that spaces and underlines are invalid, but dashes are OK?

spaces, dashes and underlines are invalid, how does one validation for these 3 conditions

I'm sorry, I don't understand. Your sample job numbers have dashes in them, but you're saying that dashes are invalid. Do you want to allow the user to enter the job number with the dashes and then strip them out, or do you want to prevent the dashes being input, or what?

Try a validation rule of
Not Like "*[-_ ]*"