After running top, do SHIFT + m (i.e. Uppercase M).

From man top

SORTING of task window
  For compatibility, this top supports most of the former top sort keys.
  Since this is primarily a service to former top users, these commands do
  not appear on any help screen.
    command   sorted-field                  supported
      A         start time (non-display)      No
      M         %MEM                          Yes
      N         PID                           Yes
      P         %CPU                          Yes
      T         TIME+                         Yes

So SHIFT + t would sort by running time.

Once you have the pid and want to investigate further, do ps -o cmd fp PID to find out what’s the corresponding command.

Ref:
https://unix.stackexchange.com/questions/128953/how-to-display-top-results-sorted-by-memory-usage-in-real-time
https://stackoverflow.com/questions/4802481/how-to-see-top-processes-sorted-by-actual-memory-usage
https://serverfault.com/questions/479460/find-command-from-pid