That one below your ears is probably one of the most dangerous pressure points around. Be very careful with that one as you can seriously damage someone. For this reason I would not like to provide further descriptions, but instead leave it up to your sensei to take responsibility for any instruction.
Pressure points are not always great for controlling people (as they tend to just wriggle around trying to avoid the pain), and as mentioned above, sometimes they are ineffective because of the particular physiology of the person making it difficult to locate it exactly. However striking pressure points hard can and have killed people, and even pressing on certain ones hard can cause temporary and even permanent damage.