In that case, I have included the referenced sequence diagram in another sequence diagram using ref in sequence diagrams. You can do that. You can make daigram 1 and use it it wherever its required in another sequence diagram.
if "in-house pricing system" is within the same company/organization then it can be within the network, but it could be on different server. It is not necessary that JMS application is within the same app server. You can put your findings/assumptions in your notes/assumptions section.
if you have more knowledge about multi tier architectures, NFR's, and other skills required for part 1, you can just keep practicing mock-up exams, then you should be fine. SCEA study guide (Cade) is not enough. Also search web for more questions.
Do i need to show the external systems in the class diagram ?? or is it okay to add comment the class diagram ??? There is no need to show external systems in the class diagram, I think its better to show it in comments.
how to show these systems in the deployment diagram Since its external system and you are not deploying in your servers, I think there is no need to show external system in deployment diagram.
We need to do the essay to our assignment be graded, correct?Yes So if i fail at the assignment i need to resubmit assignment and do the essay again too?Yes and No, resbmit the assignment and no need to take essay again