The question is ambiguous. If you are referring to Construct 2's runtime code, that is not GPL-licensed (nor under any open-source license, despite being unprotected in the install directory), nor can anyone re-license it, but it is (obviously) permitted to be republished at will royalty-free with commercial use. If you are referring to your own Construct 2 project data (the .capx/folder project), you can license it however you like, but I'd have thought that was obvious, it's your work!