Am I allowed to ask questions related to "what can I do with this knowledge for" theme on Stack Overflow? Of course, in the topic of programming.
Questions related to career advice would mostly solicit opinion-based answers which do not fit in the Stack Exchange model of Q&A.
Also, such question may not help future visitors either. Some related discussion on Are Career Advice questions useful to anyone except the poster?
Questions related to programming are welcome here! Anything that you are trying, and is not working would have an answer here.
But this community (Stackoverflow) has some rules. Which are fairly described on the about page as:
So, you will not ask for recommendations or you will not start any poll or ask for opinions. As far as discussion is related, you can start a long discussion in Chat rooms here: http://chat.stackoverflow.com/. This chat site is designed for programmers who want to discuss about what this code works and how.
Secondly, your question
"what can I do with this knowledge for"
Contains a poll or opinion type thing. You can ask for a code, if you have a piece of code you can ask what can I do to make this code work, but not to ask for something like, I have an idea on my mind, what code can do this job.
To ask questions that are opinion based, or when you need some help from others or when you want a suggestion you can always go to programmers.stackexchange.com. This is the site, where you can ask questions which have anything related to suggestions or asking for what method would be best to do this!
Good luck! Cheers.