You can validate available domains with an API catalog for WRS endpoints is now available from the Windchill 11.2.0.0 client customization documentation page
API catalog for WRS endpoints at client customization documentation page does not contain all the endpoints available. It contains only endpoints defined at folder path <WT_HOME>/codebase/src/rest/ptc/doc. Moreover, it will show you up to 3 levels of navigation level. The complete list of endpoint available can be found at URL <Windchill>:<port>/Windchill/servlet/odata/<domain>/$metadata.
As of Windchill REST Services (WRS) 1.5, there is no OOTP domain for ProjectLink. However, you can add/configure it as a custom domain.
Path should be without src: <WT_HOME>/codebase/rest/ptc/doc
You can change a navigationLevel parameter in <WT_HOME>/codebase/rest/ptc/doc/config.*json "navigationLevel" : 1, the maximum value is 3, overwise you get performance issue, may be need MethodServer restart.