How to make an enemy ai?

a few more tutorials that may help you on your way:

https://wiki.unrealengine/AI_Bot:_Blueprint_Scripting_Playlist

https://wiki.unrealengine/Create_An_AI_Bot_in_Blueprint

https://wiki.unrealengine/Unreal_Engine_AI_Tutorial_-_1_-_Making_AI_Jump_as_a_Part_of_Path_Following

https://wiki.unrealengine/Unreal_Engine_AI_Tutorial_-_2_-_Avoidance

https://wiki.unrealengine/Unreal_Engine_AI_Tutorial_-_3_-_Random_Wandering