I smoked two cigarettes. Will it show up on a urine test 4 days later?

Depends on the test. If you smoked tobacco cigarettes, then the answer is no, since this is not tested for in any standard urinalysis or toxicology screen. If you smoked marijuana, then a urine drug screen will almost always be positive for thc 4 days later. A regular physician urine dipstick and urinalysis does not look for drugs, so the test must be a specific urine drug test.