Naka is the suffix to make your conversation more politely.
"Thanks ka" is Thinglish (Thai+English). To add the word 'ka' is a way to express one's politeness. If the speaker is a lady, she will utter the word 'ka'.
It is a kindness way of Thai speaking culture when you want to pay the respect to the ones you talk to. The meaning is just like''sir''in English.