The edges, vertices, properties and indexes are stored in a fixed table and a fixed set of column families within the table in HBase. i.e. edges are in one CF, properties are in another CF.
They are linked via the rowkey / ID.
It is probably not clearly documented anywhere. You may need to look into the org.janusgraph.diskstorage.hbase package.
Also you can start up JanusGraph with HBase, create the sample graph. Then look at and scan the table to get a feeling.
