yapıyorsun

you are doing

So when someone says 'sen ne yapıyorsun' does this means 'Are you doing anything?'

Thanks.

What are you doing:

sen : you
ne: what
yapıyorsun: you are doing.

The first "sen" isn't totally necessary in the sentence as we have the "sun" ending on "yapıyor" which shows it is you we are talking about.

"ne yapıyorsun" is enough to say "what are you doing".

Putting "sen ne yapıyorsun" either makes it clearer, or is used to emphasise the you bit, e.g. If they have said what they are doing, they might ask "sen ne yapıyorsun" what are YOU doing.