This question already has an answer here:
I am wondering what technology is used in Stack Exchange to create the graphs like "reputation graph" in the network profile. Is it Highcharts?
Yes, it is.
Seeing as we have a
The source code is your friend.
Since you already have an idea of what you are looking for, all you need to do is confirm: view source for the page and search for "highcharts". What do you know, there are hits for that term in the source. I think you have your answer.
For most questions of this nature, the fastest way to get an answer is to look at the source. If the answer had not been high charts, you would have needed to find the actual graph item in the DOM and looked for namespace clues or reviewed the list of JS includes. Not the five seconds it took to confirm an answer you already guessed, but still not very long.