Hello from JustAnswer.
There have been some isolated case reports of amoxicillin causing a false positive on urine drug screens for cocaine, although there also have been studies on groups of patients that failed to show that it would do so. Isolated case reports are not a good method of proving that drugs cause false positive results, because some false positives will occur in anybody, including people that are taking no drugs of any kind. So, it could be a coincidence that the test was falsely positive in the isolated case reports.
However, even if there is a low rate of false positives on a urine drug screening test, there is no reason to avoid taking amoxicillin because you work in a job at which drug testing occurs. You can insist that a confirmatory test be done, and the amoxicillin clearly will not cause a false positive result on a confirmatory drug test.
So, there is only scant evidence that amoxicillin will cause a false positive screening test for cocaine, and that may have been due to coincidence. But even if not a coincidence, there is no reason to avoid the amoxicillin, because you can request a confirmatory test that will clearly not be affected by the amoxicillin.
If I can provide any additional information, please let me know.