If there are amounts in boxes 17 and 18, you will need to contact your employer to get the state tax ID. If boxes 17 and 18 are blank, you can leave the whole line blank on TurboTax - but the income will still be taxable on your Maryland return.
Maryland and Pennsylvania have a reciprocal agreement, so you would not need to file a Pennsylvania return unless there was tax withheld from your paycheck. In that case, you'd need to file a nonresident return and allocate zero income to Pennsylvania to get a refund of your withholding.