Is it possible to make joins with NQSQL without CMISQL? I'm using Nuxeo 6.0. I checked this post pretty old one, it says that it's not possible.
No, JOINs are not available in NXQL and will never be, in large part because we can't support them on databases like MongoDB and other future NoSQL databases we may use.
If you absolutely need JOINs you'll have to use CMISQL and the proper configuration to enable JOINs with CMISQL (see NXP-14979).