Hello Nguyen Dat tai,
do you want to show only popular car categories or popular listings?
I don't understand you more and more?
If you want to show only popular categories you cannot do it right now because in flynax system doesn't exist counter for categories only for listings.
At 1-st you should create functional for visitors counter for categories and then you can show popular categories. Will be better you create a new ticket with your request but it will cost you some extra.