There are four ways to find the glibc version that is installed in the system.
1. Open a terminal and run
Which should give an output like
Indicating the glibc version is 2.11.3.
2. The second method is by writing a program for it.
and execute it
Note: You might get a different output based on your version.
3. Open a terminal and run the command
4. The fourth rather crude way which would work if are running debian based systems is to open the synaptic package manager and go to the package libc-bin and see the installed version number in front of it.