I have a domain, hosted zone in AWS, lets say its example.com
I've tried adding a CNAME record for subdomain support.example.com
which points to example.zendesk.com/hc/en-us
It is not redirecting to my Zendesk landing page.
How can i get my subdomain to point to zendesk?
This is not how CNAMES or DNS would work.
A CNAME record can only point to a different A Record entry.
So for your example.com the valid CNAME entry for your DNS record can only be example.zendesk.com and you can not add the '/ch/en-us' part.
Have you looked at the Zendesk support system to see what they have to say that you should be adding to your DNS?
Looks like they call it Host Mapping https://support.zendesk.com/hc/en-us/articles/203664356-Host-mapping-Changing-the-URL-of-your-help-center