35 weeks pregnant I poked my belly button on metal door jam did I hurt my baby?

Probably not. Your baby is well protected by your skin layer, uterine layer, and amniotic fluid. A bump from a door jam is unlikely to generate enough force to cause damage. However, go to l&d if you have decreased fetal movements, cramping, pain that is increasing, or any vaginal bleeding. Even though unlikely, an abruption (placental separation)is what we worry about from any trauma. Check with your OB too.
Insulated from event. It is likely that the force of your injury dissipated within the multiple areas of insulation a fetus has in the womb. The sac of fluid has some give & would deflect much of the impact. If you had spotting after the event or notices a change in the level of movement it might indicate a problem. I would call your OB & review the specifics of your case to be sure.

Related Questions

I am 35 weeks pregnant and I have a small knot 4 or 5 inches below my belly button that is numb. Roughly size of 50 cent piece. Is it serious?

Probably not. Talk to you doc next appointment but if it's not painful it probably isn't anything serious.
probably a hernia. Likely an insignificant hernia. If it becomes painful, grows, or symptoms of bowel obstruction develop (such as vomiting, diarrhea, constipation, pain, & distension)... Then you should get out checked before your next OB appointment.