Best way to determine a bottleneck

no

but if you list your specs there are people posting here who can give you insights into how to improve your computer

You can start by running Task manager and clicking on the performance tab. If the cores are consistently running below 50%, your CPU probably isn't a bottleneck. If you have free memory, RAM probably isn't a bottleneck. Anything that hits your HD a lot will almost certainly be a bottleneck, but most games won't do this. There's not much you can do about that other than getting a sold state drive. If everything looks good and your game runs sluggishly, the problem is likely your video card.