Hello there again!
I’m trying to reduce the number of events in my game…
How do you read an object variable in the event?
I have 39 doors in my character selection screen and they all have a different object variable (1 to 39) . How can i make gdevelop know that the player clik on the door number 5 and not the number 20 ( for exemple).
For now i have 1 event for each door and i would like to make 1 event for all of them…
Hope you understand what i mean 
You have to use the expressions:
MyObject.Variable(MyVariable)to read numbers and:
MyObject.VariableString(MyVariable)to read string values.
No idea how you’ve called your object variables, but imagine you’ve set a different variable “destiny” to each door object, the door with variable “destiny” = 5 means that clicking on it will move you to the fifth level. And you conveniently called the scenes like this: “Level1”, “Level2”, etc., so the fifth level is called “Level5”.
So far so good, with this perfectly made structure you can do it:
Conditions: Left mouse button pressed
Cursor is over Door
Actions: Change to scene "Level" + ToString(Door.Variable(destiny))
If you click on the fifth door, Door.Variable(destiny) is = 5, then ToString(Door.Variable(destiny)) = “5” and finally you can concatenate strings, so “Level” + “5” is = “Level5” 
You can make it even easier if you set the variable “destiny” as a string variable with the name of the scene the door has to go, for example to the fifth door the variable “destiny” would be = “Level5”, then in events the action would turn into:
Change to scene Door.VariableString(destiny)All this assuming you want to change scenes… because you’re talking about doors. But you get the idea, it will work anywhere 
Success with your help thanks!