The Frostmarch event card, Howl of the Wendigo, states: "All characters , no matter what Region they are in, must attack a character they land on. If a character defeats another character , he must choose to take a life as his reward . Once this happens, the Howl then echoes to the discard pile. "

Question: When two characters are on the same space in the inner region, does Howl of the Wendigo apply ... must they fight? Base rules state that characters cannot encounter one another in the inner region except for Plain of Peril, Valley of Fire, or COC. And if they do have to fight, does the character that landed there still have to encounter the space as well?

No. Howl shouldn't have any effect if the characters are not on the Plain of Peril, Valley of Fire, or COC. - If that were the case, you could use it to skip spaces you'd rather not encounter. (Besides, this seems to be another case of "can't" trumps "must". -- Base Rules, P. 15)