Follow the instructions provided in the README, once the notebook launched in browser, enter the following config and execute
Janus Graph configuration
%%graph_notebook_config
{
"host": "localhost",
"port": 8182,
"ssl": false,
"gremlin": {
"traversal_source": "g",
"username": "",
"password": "",
"message_serializer": "graphsonv3"
}
}