You don’t need to create any gzipped file. If you use “dot” in the -r flag Dgraph will seek for RDF, GZ or any other type compatible.
e.g:
./dgraph bulk -r . -s 1million.schema --zero localhost:5080 --map_shards=4 --reduce_shards=2
Just use the same Blank node in all RDFs - check this part of the tour A Tour of Dgraph