You will file a non-resident income tax return for Pennsylvania and a resident tax return for Delaware.
See : Delaware on Out of State Income
Where do I put the credit for the tax that I paid in Pennsylvania on the Delaware state tax form? I haven't been able to find it.
It should automatically put in the credit if you complete My Information correctly. Make sure you have your residence of Delaware and that you earned income in Pennsylvania. When you enter your W2 in the Income section, make sure you include the taxes withheld by PA. When I did a test, I received a refund of most of the taxes withheld by PA and the Delaware tax owed went down significantly.