So the question is, basically, how to know if you are ready for the exam. If you haven't already, grab the list of "Skills Measured":
http://www.microsoft.com/learning/en-us/exam-70-461.aspx
Examine all the points one by one and think carefully about how confident you are that you knon the subject matter. If you know all of them except for XML, then you should still be able to pass the exam, because it is not heavy on XML (only a single entry
out of the whole list of Skills).
If you want to learn a bit more about XML in SQL Server, read the articles from Technet, such as:
http://technet.microsoft.com/en-us/library/ms190936(v=sql.90).aspx
http://technet.microsoft.com/en-us/library/ms189887(v=sql.105).aspx
(The previous links are for older versions of SQL Server, but the content is still valid for 2012).
If you are still unsure, you can take a practice test from a provider such as MeasureUp (linked from the exam page), but in my personal opinion it is not worth your time; I prefer to just go and take the real exam, even if it is more expensive than the practice
test.