Query on SQL Server Always On DC1: (servers are in WSFC): DB_Server1 and DB_Server2

DC2: DB_Server3

DC1 and DC2 servers are located in different geo locations. Is it possible to configure SQL 2017 Always-On/SQL 2017 Distributed Always-On in above environmnet? 
As per my understanding, the servers should be in WSFC, but DC2 DB server is not in cluster, its standalone machine. If it's not possible to configure SQL always-On in above env, please suggest which SQL HA/DR solution i can use...
This is not enough information in your question, to definatively say if you can or can not meet your goal with your available resources.

It is possible to Create a domain-independent availability group that spans physical locations.

Yes it can be done.  How to set up the infrastructure to support it, is going to be out of scope for DBA.se, but you can get help at https://serverfault.com/help/on-topic &amp; https://networkengineering.stackexchange.com/