Hi,
I am looking if there are any proper guidelines for integrating webhook in TheThingsNetwork Gateway for getting data?
Thank you.
So you did bother to look through the “Learn” section linked from every page (^above), right? As a new user I would highly recommend you take a bit of time to read up 
To save you a few clicks (<hand full) link to right general area here…
https://www.thethingsindustries.com/docs/integrations/webhooks/
Note: Webhooks and integrations associated with Nodes (Devices) ( & under Applications) not the Gateways (I see you called out RAK specifically in sub-category but same goes for all types).
To directly answer the question:
There are no guidelines because you can’t.
There aren’t any guidelines for implementing web hooks either - you sort of just implement them using the tools provided to suit the end point you are targeting.
Like many of these sorts of queries, it would be soooooo much easier if you explained what you are trying to do so we can be specific.