How do I track from which source/medium did the customers got to know about my product ? I am running facebook ads, Google ads and LinkedIn posts. I need to know what path or how did user came to know about my product. Is it through FB ADs, Google ADs or through Organic content ? How can I track this ?

Ask your customer

UTM parameters need to be added to your ad URLs then you track them at GA level.

I need to know if the user came to know about my product through facebook or linkedin, before they convert

You need to mention source in your utm parameter

If I read the question exactly as you phrased it, my answer would be that the answer can be only given by the contact - even then it would be vague

Use https://utmbuilder.net/ to generate UTM mention source and medium Example: https://www.example.com/?utm_source=google&utm_medium=cpc

I also think attribution could be a factor too here amongst the channels, If am not wrong attribution is just not for conversions only.