Is it souse chef or sous chef?

It depends on the circumstance. If the sous-chef outranks you, it is not necessarily wrong to address them as "Chef". Usually the title is reserved for the Executive Chef or Head Chef, and addressing one of their subordinates as "Chef" in their presence could be perceived as an insult. It depends on the kitchen dynamic (formal/informal), and the ego of the chefs you work with!

If the Sous Chef is taking over due to the Executive Chef being absent then calling him/her "Chef" is acceptable.

* I would always address my Sous Chef as chef. There can be more than one person called Chef in a kitchen. Chefs due call each other Chef in a working situation. But I also agree with the above that it greatly depends on the kitchen dynamic. And the egos!