There's this thing called Knowledge Center at
It has a search capability where you could enter that (see top right)
If it is a command it now even has a drop down by the command description
with different help available based on the version of OS you are asking
For example the drop down for SNDDST goes all the way back to V5R4. That
seems to be the earliest that Knowledge Center covers.
One particular command of interest I see the drop down only goes back to
7.2 so I assume that the command was not available prior to that. The
answer might be "upgrade to 7.2 or higher" then.
Hey if I come across as short, I'm sorry. In my defense I did spend
yesterday at the regional burn center getting my skin scraped off.