You can make combinations by adding several conditions, so if you want to make it so the character jump forward when Right arrow and top arrow is down, you can add 2 events, I guess you can use keycodes as well. Anyway here is how you can do it:
Both event do the same, so making a function to handle the actual jump would be best. But If you are not sure how to use functions you can just copy/paste one to the other so they are the same.
Event 1:
On Right arrow pressed (Trigger)
Key Top arrow is down
Actions:
jump forward right
Event 2:
On Top arrow pressed (Trigger)
Key Right arrow Is down
Actions:
jump forward right
Then you just make one for the left as well. The reason you make 2 for each side is just to make sure that the player doesn't have to be precise when wanting to jump forward. But you could probably get by just using the first event, if you don't care to much.
Or you can make if so:
Event:
On Right arrow down
On Top arrow down
That would work as well and is probably the best way, as players are most likely moving when they want to jump anyway