The completed diagram looks like this:

On the left, there is a triangle that is obtuse and isosceles (and thus not scalene)

Next, there is a triangle that is both obtuse and scalene

Next there is a triangle that is scalene, and acute (and thus not obtuse)

On the far right there is a triangle that is isosceles and acute, and thus neither scalene nor obtuse

To do this sort of problem it is important that you identify what properties the triangles should have in each part of the diagram. So the overlap must have both properties:

A triangle in here must be bothe obtuse and scalene

A triangle in here must be obtuse, but it can't be scalene (because it's not in the scalene circle)

A triangle in here must be scalene, but it can't be obtuse

A triangle out here can't be obtuse and it can't be scalene