Hold the 'o' in the 'bo' for an extra beat, then "ken" and "ka" as you'd expect them to be, and you've pronounced it. Your instinct is probably to put the stress on the 'ken' (boKENka), do that but maintain the stress through the 'ka' (boKENKA) and you get extra "pitch accent" credit
The kanji for it would be 冒険家, individually meaning "dare", "risky", and "house" or "professional" -- you'll find the 冒険 (bouken) in a lot of video games, like here, because that's the "adventure" part!
Not to say you should adopt it as a name or anything, but now you know some extra facts about it