Where can I find which version of DSS I have installed (enterprise edition)?

UserBird

I presume it's in the administration settings somewhere but I can't seem to spot it.

AdrienL

Click the question mark in the top-right corner, then go to the bottom: About.

Martin_Vlčko

For others who look for DSS Free version.
Administration icon in the top-right corner -> Maintenance -> System info -> DSS version row