You can find out how much total memory ASE is allocated by looking at "total memory" in sp_configure. However this isn't quite the same thing as RAM (physical memory) usage, at any given time the OS may be swapping ASE's memory in or out of RAM, and I don't know how to get a report on that.
It may be possible to lock ASE's shared memory into RAM using sp_configure "lock shared memory." See "lock shared memory"