I helped in the implementation of a friend's project by doing some coding work, but did not get an acknowledgement of it in his research paper, tied with the thesis. How can I claim my right? I actually wrote a module for him.
You wrote the code for him - on the face of it, you own the copyright and allowed him to use it for the purpose for which it was written. Unless you required him to acknowledge your contribution in some way there is no legal requirement for him to do so.
Universities usually require candidates to identify significant contributions to the work by third parties. Significant usually relates to the main thrust of the academic work so it depends what your contribution was and what the thesis was about to see if you should have been acknowledged. However, this is a matter of academic (mis)conduct, not law.