What's it called when you like to do something because you're skilled at it? My searches didn't yield much but I watched a presentation with this term in it and I can't remember what it was.
I would be inclined to guess that the presentation you watched was on the concept of flow. The Wikipedia entry for flow introduces the idea this way:
In positive psychology, flow, also known as the zone, is the mental state of operation in which a person performing an activity is fully immersed in a feeling of energized focus, full involvement, and enjoyment in the process of the activity. In essence, flow is characterized by complete absorption in what one does. Named by Mihály Csíkszentmihályi, the concept has been widely referenced across a variety of fields (and has an especially big recognition in occupational therapy)...
Flow involves more than merely liking to do something because you're good at it, so if you are looking for a term that calls out and is restricted to this single element, flow isn't it.
A associated word, and a component of flow is the adjective, autotelic. The Oxford Dictionaries site offers this definition:
(of an activity or a creative work) having an end or purpose in itself.
Although not exactly what you asked, this word perhaps comes close to embodying the notion of work that is "its own reward".