Why do you want to know? Probably because your system is swapping, which makes it slow, and you want to find the culprit.
But: A particularly process or program doesn't decide to use swap. It decides to use memory. The OS (kernel) then decides which pages to swap out. And the process that gets swapped heavily is not necessarily the culprit, but might be the innocent victim. From that viewpoint, the correct thing to look at is total memory usage of processes, not swap.
Second: Using swap is not necessarily bad, on the contrary: it removes pressure on memory, allowing the system to be faster. What is bad i heavy swapping, where memory pages have to be copied to and from disk all the time. I could put the same thing this way: Swapping out (writing to disk) is neutral to good; swapping in (reading from disk) is bad. Looking at the amount of swap space a process uses may be misleading.
