A no code solution would be to assign each enemy a point or a coin then use the Event Observer and monitor the points/coins detected in the Session Total which would trigger level complete.
If the number of enemies is created randomly then my no code solution won’t work. You would have to set the number to a specific value for the no code method to work. Your scenario would require some coding.
Increment a global variable (or local) each time you spawn an enemies and decrease that value each time an enemies dies. When that value is 0 then the level is completed. Link the condition to a timer that has 9999 value or something that fit's your gameplay style and check if the value is 0 every 1 second or more depending on your game.
Here is an in depth tutorial explaining how object count could be done with any number of randomly spawned onjects, Hope this helps solve the problem. bbdoc also included in the video description.