My ten year old son has a painful bump on bone right behind right ear. it is not red or bruised. should i take him to er?

I wouldn't: This is a probably just a lymph gland that has reacted to a local skin irritation or simple illness. If it bothers you call your doctors service and discuss it with their staff.

Lymph node: This is likely an inflamed lymph node and being tender is a good sign. He must be fighting an infection. Observe, drink plenty of water and see if goes away. After it has done its job.