One of the most important activities for your PMP Exam Prep is to take mock exams. Be sure that you do this only after reading the PMBOK® Guide at least once. Also remember that failing mock quizzes does not mean you will fail the PMP exam. Online sample exams should be used as a progress indicator in your preparation. Nothing more.
Most students tell me that they repeated their sample exams again and again until they were satisfied with the results. There is a danger in that approach: when you take the same sample exam again and again you will start to remember the questions. You will remember that you answered B in your last attempt, and that the correct answer is C. This means your result will improve every time you repeat the same sample exam.
But on the PMP Exam you only have one chance!
So my recommendation is this: Sign up for an online PMP Exam simulator. This simulator will cost you some additional money, but their two major benefits are that they offer a large number of questions & quizzes that you can take (no repetition!) and they allow you to test yourself in an environment that closely resembles the actual PMP Exam.
Therefore, go beyond searching for free PMP Exam questions on the internet and use the professional tools that are available to you.