In Help/About, of course, like any other program!
Oh...wait...
In SEPM, click Admin\Servers\Local Site\<ServerName>. The version is in the right pane.
11.0.4205.75 = MR4 MP2
11.0.4014.26 = MR4 MP1A
11.0.4000.2295 = MR4
11.0.2010.7 = MR2 MP1
Don't have any other versions on my Secret Version-to-MR/MP Decoder Ring, but if you post your version number, someone will recognize it.