Displacement is just the distance between the start-point and the end-point, regardless of the route that was traveled on the way.
If you're asked to find a displacement, then the first thing the asker has to do is define the part of the graph that he's interested in.The easiest way to do that is to specify the start-time and end-time. Once you have those, the displacement is easy. Just look at the graph. Find the position at the end, and the position at the beginning. Subtract the beginning position from the ending position, and that's the displacement.
Ignore everything in between. No matter how many curves, curls, breaks, or stops the graph may have on the way, you don't care. The displacement is just the difference between the end position and the start position.
