When playing with both the Cities & Knights expansion and the Volcano variant, can a volcano eruption destroy a player's knight? (Knights occupy intersections, so theoretically the lava could flow down upon them.)
There's a German Q&A on this subject that says Knights are unaffected by volcanic eruptions. The reason for this is simply stated as "Because the rules on eruptions only describe the effects on settlements and cities, you can conclude that nothing happens to knights."
I find this answer quite unsatisfactory, and I recommend that you decide before the game starts how to handle this occurrence. Personally I prefer to think that the volcano drives knights away. The owner then has to move the knight to a different intersection, taking all relevant rules into consideration.