Dear Haseeb, although I'm not a Masters in Urdu, yet regarding your query, I wanna say that those types of Urdu Essays remain part of every paper. One is about Current Affairs, and the second is related to Urdu Adab. So, you should also cover all topics related to these two major aspects. For Current Affairs related topics, you yourself can decide the topics or cover those topics which you also going to prepare for English Essay. Environmental Problem, Judicial System, India Factor, Education and so on can be very handy to be prepared. While, for Urdu Adab, Ghalib's poetic style, Short evolution history of Urdu literature, Problems related to Urdu language's promotion and efforts made for this can be very helpful to prepare.
Lastly, I would also suggest you to buy Caravan Publishers's "Caravan Urdu" exclusively written and recently published for PCS/PMS exams. This is the single book that I've found to cater the needs for aspirants of PCS/PMS like you and me. Best wishes!

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"But screw your courage to the sticking place,
And we'll not fail." _Shakespeare, 'Macbeth')