If you took one Seroquel on a Thursday night... and then had a urine drug screen test for pre employment on Tuesday morning, would the Seroquel show up in the drug test?

Did you have a prescription?

Why would you take just one? It's one of those psychiatric drugs that has to build up over days and weeks, and monitored. It's an anti-psychotic which helps some people with sleep too.
So if you were taking it over time and Thursday was your last day, yes, I think it will show (but don't know for sure - it's not a drug people abuse).
If you took just one ever, no I don't think it will. Depends on the milligrams.
If you have been taking it all along as prescribed, it is foolish and dangerous to go cold turkey.
So this just isn't making sense.