Wearing Cap / Topi In Namaz
To my understanding a cap used to be a sign of respect, so people wore it to show their reverence and respect to Allah. There are some cultures where removing cap is a sign of respect, so I guess a person praying to Allah need to remove cap when praying. I guess whatever the culture may have the sign to show repect, we should show such respect in prayer. A universal sign of respect is to have clean clothes and clean body.