I had just used EJBs as a client till now, had not implemented myself.
I prepared myself around 3 to 4 weeks.4-5 hours per day. I should admit that there were quite tricky questions. I used Cade as base, McGraw Hill's Allen&Bambara book also in advance.
Whizlabs Tests are quite comparable to the exact exam, where IneSystems exams are harder(I got 28-32 at IneSystems)
But at the same time, the wording was in some questions very un-clear. and 2 questions were wrong imho. even there was a sequence diagram and it asked the diagram type, the answers being sequence diagram and interaction diagram. but seq. is already sort of interaction. in a radiobutton question, this shouldn't happen , right?
As to your question, there is no "interaction diagram" per se in UML. There are two dynamic/interaction diagrams which are called "sequence diagram" and "collaboration diagram", and they are isomorphic.