Question
Hello,
Can  I plant grass seed over dead sod or do I NEED to remove the sod first?

Answer
Any Seed you use is going to need close, constant contact with Soil and moisture to germinate successfully.  I would till it in, breaking up clumps and removing debris, then rake smooth and even.  A top dressing of Compost or Manure is not a bad practice, either.

If your Soil is rich and healthy, and you have a good supply of Earthworms, they will accelerate the decomposing of the old Sod while your new Seed becomes established.  I would elaborate, but you did not mention where you are writing from.  This is a good time to plant Cool Season Grass.