Some people pronounce the sentence "How are you feeling now?" as How're u feeling now? where the the word "are" vanishes from the sentence while speaking. Some may pronounce the Sentence "How do you feel?" as "How due feel?". It often happens in daily life and do not bother. Ofcourse they might have well known about this.
While 'how you feeling now?' is grammatically incorrect because the verb is missing, you will hear native speakers using it colloquially. Quite often auxiliary verbs are l;eft out- 'You OK?', etc. In formal settings or written language, it would be considered an error. Also, as Chattogokul says, the auxiliary verb can almost disappear in many speakers' speech.