Is it possible for a node to host multiple cluster in relation to Always On AG In my example, I have 3 database servers with their own DR servers, own availability group, own clusters.  Is it possible to setup another server which can be part of the 3 clusters and be a secondary replica on each of them?
Taking from your last comment


  yeah im asking if each of the primary replica in each cluster can create a secondary replica in a new server. even though each are coming from different clusters. can the server (to the most left) be on each of the cluster?


This is possible but you would have to use Distributed Availability groups and should have Windows Server 2016 or above as OS. 

Also note that the third server cannot be part of all WSFC(Cluster 1,2 ,3). If you want to achieve what you need you would have to create new WSFC and add new machine as part of it. Now you can configure distributed AG's to achieve what you need.