What part of Solaris version string IDs the update?

s10s_u10wos_17b the u<#> is the update version. So that is Solaris 10 Update 10.

The line in /etc/release shows it was built in august 2011 and contains s10s_u10wos_17b which reads: Solaris 10 for SPARC (would be s10x for x86), update 10, "wad of stuff" (just means it's not the initial release), 17th build since u10 development started, second respin (b).

Note that this doesn't reflect an update that has been applied or not to the server but the precise version of Solaris that was initially installed on that machine.

Kernel updates can be identified with the kernel patch version, here (147440-01) which is the one delivered with u10. That means it wasn't updated (patched).

Should you have patched the OS, an additional line would have appeared at the end of the file telling what Solaris update the update match.