I went through the concepts,I wrote exam using pyspark,so you should have the idea of python. Then prepared Spark ,took Durga Sir's CCA175 course. That gives you 95% preparation for exam,it provides both concepts and excercises at the end of the course. I practice them a lot, when I felt I lost some concepts,I went back in the course and gone throught the concepts again. Practiced the excercies repeatedly to maintain the time,as it's crucial during the exam. I practiced Navneeth Kaur's exam papers ,and some other dumps I found online. Learnt many new things while practicing them too.
Durga Sir,keeps his course uptodate,so you can take his course CCA175,python/scala. I haven't used any RRDs or relied on spark 1.6.
In exam you have to use either python or scala languages. I solved all my questions using Spark DF and spark SQL.
Best of luck,prepare well. Time is crucial.