Hi,
I wnated to know if I can replce glue contact with a RB2 (node to node), CGAP (node to node ) or simply by doing a node equivalence between two surfaces.
Why don't you better open at least QRG and check the differences between these elements and their abilities?
It's hard to help you without basic info - what solver / analysis, expectation, purpose of simulation...
To add on janFEA's point the Nastran Element Library Reference will have some more info on RBE2/RBE3 elements(7.5 & 7.6) and Gap elements (6.5). You can access the QRG and Element Library Reference through the FEMAP command Help > NX Nastran.