AFAICT:

 

Look in /lib, and I think the library itself has the version number in the name.

 

I think there will be a bunch of files called libc.so.[partial version number], all linked to the file which has the actual version number for the end of the name.

 

The filename may not be that, I haven't cared what version I had since the libc5-libc6 transition (the WordPerfect binaries required some libc5 libraries or something, so they kept bombing)