How can I find all of the domains pointed to my IP address?

The best way to locate all of the domains attached to your IP address is to use an online tool. For example, here's one that I use:

https://reverseip.domaintools.com

Edit: This site is an alternative to the above in case the original site isn't working for you. It should also be noted that finding all domains associated with an IP is tricky due to the way DNS works and the fact that DNS can be quickly updated, so don't be surprised if online tools like the ones I've linked aren't 100% accurate.

Another tool you can use if you're into command line is dig. Dig will allow you to either look for the IP of a domain, or for the domain's reverse DNS record. For example:

dig lindude.com +short
45.56.103.14

dig -x 45.56.103.14 +short
lindude.com

As you can see, the -x flag allows you to perform a reverse search on an IP.

Dig is limited since we only allow a single PTR record per IP address. If you have 2 or more domains attached to an IP, then dig -xwill only show the domain set as a PTR record. You'll want to use the online tool I linked above if you need to find all domains pointed to an IP address.

If you're looking to set rDNS for your Linode, then check out this guide.