What tool can i used to take the bolt from the valve cover for 2006 Suzuki forenza and when the engine run the coolant leak at the back of the engine so what is the problems for the leakage for the coolant

We don't have the specifications in our database but for valve cover removal, basic box and sockets would be sufficient.

You need to locate the source of the leak as we can't see it from here.

i want to remove the vavle cover gasket and i am not sure of the tool size
and there is a leak at the back of the engine which means when the engine
is running the water or coolant will be leaking

Valve covers bolts are mostly 10 mm hex heads.
You need to visually locate the source of the leak. We can't help you on this and telling you possibilities does not help.