I was laid off from a position in PA but I now work in NY. Can I claim unemployment from PA while still working in NY?

No. Once you return to work you can't claim anything. UI is a federal program, only administered by the states. To be able to claim unemployment you must certify that you were ready and able to work during the period. If you have a job you would be perjuring yourself to collect.

IF your earnings are under the allowed. You have to report any earnings you made for the week. If you received any unemployment for a week where you earned money, that is a fraud, If you earned over the amount allowed, not only will will have to repay the unemployment you received but can even be charged with a crime.
So as soon as you started work in NY, you had to start claiming that income.

Don't even think about trying to collect UE from another state as they will catch you and for each week you claim and collected UE benefits would be one count of fraud.