[chimprich]

You probably wouldn't be able to for sure but if you had no more unexplained phenomena around then you'd probably have a reasonable idea.

Of course that only applies to the laws of physics. You'd still have an effectively infinite universe of maths, geography, biology, etc. to explore.

[zaarn]

You would still not know. Maybe there is a branch of physics that you're simply biologically not equipped to even perceive, comprehend or understand in the slightest. Maybe not. The point is that you can't know. Not too long back, people thought gravity as entirely newtonian and couldn't imagine that gravity could behave like waves. Or that particles can exist as both particle and wave.

IMO the limit of knowledge is simply the limit of information you can cram into a region of space without it collapsing into a blackhole because of that.