Frankincense is a Alchemy Material in Kingdom Come: Deliverance.
"Often used in various religious ceremonies and during meditation. In antiquity it began to be used by Eastern Christians, who later passed it on to their Western counterparts. Frankincense has a relaxing effect on the human body and can improve one's mood and concentration. But it also has psychoactive effects, which explains why it is primarily used in religious rites and magic elixirs."
Frankincense can be acquired at the following locations