You can apply some frankincense oil directly on your skin however it's best to dilute the frankincense oil or other essential oils in some carrier oil such as olive oil or other lotion.
Applying frankincense oil directly on your skin could cause skin rashes or other skin irritation especially if you have more sensitive skin than other people.
The last time I put some frankincense oil directly on my skin it caused a slight rash but it went away within a week so now I always just dilute the frankincense oil in some olive oil or lotion before applying it to my skin.
That goes for other essential oils as well I always dilute them before applying them to my skin to avoid skin irritation and rashes.