from where should I prepare gk for cmat

Hi
The best way to start for GK for any exam is to look at the past year papers of that particular exam and get an idea about the static GK questions which have been asked in the exam in past 3-4 years, by this you will get to know about the topics which you have to cover or focus more on because GK is diverse and for current affair questions it is advisable to read daily current affairs and newspapers.
You can check past year papers here : https://cracku.in/cmat-previous-papers