Alright, I got the solution by hit and trial:
Node currentNode = kcontext.getNodeInstance().getNode();
List<Connection> inConns = currentNode.getIncomingConnections("DROOLS_DEFAULT");
Node parentNode = inConns.get(0).getFrom();
System.out.println("Current node id: "+currentNode.getId());
System.out.println("Parent node id: "+parentNode.getId());