[SOLVED] How to detect surcharge on the same task?

How can I check if one ressource is assigned on two different tasks at the same time (100%)?
For example, RR is assigned on two projects the same day (20 Oct 2015) and no alert is displayed, so what is the way to detecte it?

There is no alert because it is not an issue : resource can be affected on same period on several projects, and total affectation can be more than 100%.
You can see affectation summary on resource screen.

How to detect overload on the same ressource?

There is not overload of resource in ProjeQtOr planning !!!
If resource is planned on 2 tasks that should come same day then one of the two is extended on following days (witch is delayed depends on priority of tasks, have a look at priority in planning calculation in the user manual).

What's happen if the two activities have the same priority? ProjeQtOr choses one with "random logic" to plan?

Default priority is WBS order.