A career cluster is a collection of jobs that require similar skills and which typically are in the same field: these are jobs that one can consider changing to from the job that one already has.
let's look at the options one by one:
a collection of jobs that calls for a shared set of skills
-yes, this is what I said before!
a category of paid positions that exists within the same company
-no, positions in the same company don't require similar skills. For example, a company might employ a programmer and a Spanish translator. This is the correct answer!
a set of jobs that involves common technical training
-this, too is a career cluster
a group of occupations that requires the same educational background
-also a career cluster