"Confirm of receipt" and "treat messages" are generic names for what you can do with the messages. You can do something like this:
[{"id":"79b7eccc.7e0aa4","type":"tab","label":"Client","disabled":false,"info":""},{"id":"f52a4ff2.f5026","type":"inject","z":"79b7eccc.7e0aa4","name":"Message","topic":"","payload":"","payloadType":"date","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":140,"y":140,"wires":[["25f186d9.0cb17a"]]},{"id":"25f186d9.0cb17a","type":"queue in","z":"79b7eccc.7e0aa4","name":"queue in","config":"234672ff.22406e","sendError":true,"x":560,"y":140,"wires":[[]]},{"id":"514e8648.37a058","type":"queue out","z":"79b7eccc.7e0aa4","name":"","config":"234672ff.22406e","x":180,"y":220,"wires":[["dd0d1b35.f17ee8"]]},{"id":"bb53f59.2f93008","type":"mqtt out","z":"79b7eccc.7e0aa4","name":"Server","topic":"data","qos":"1","retain":"false","broker":"4509155d.f4762c","x":610,"y":220,"wires":[]},{"id":"dd0d1b35.f17ee8","type":"change","z":"79b7eccc.7e0aa4","name":"pack message","rules":[{"t":"set","p":"message","pt":"msg","to":"{}","tot":"json"},{"t":"set","p":"message.uuid","pt":"msg","to":"uuid","tot":"msg"},{"t":"move","p":"payload","pt":"msg","to":"message.payload","tot":"msg"},{"t":"set","p":"payload","pt":"msg","to":"message","tot":"msg"}],"action":"","property":"","from":"","to":"","reg":false,"x":420,"y":220,"wires":[["bb53f59.2f93008"]]},{"id":"aae3ea9e.d31268","type":"mqtt in","z":"79b7eccc.7e0aa4","name":"","topic":"data/ack","qos":"2","datatype":"auto","broker":"4509155d.f4762c","x":120,"y":280,"wires":[["6b40a0c8.a837e"]]},{"id":"6b40a0c8.a837e","type":"queue ack","z":"79b7eccc.7e0aa4","name":"","config":"234672ff.22406e","x":540,"y":280,"wires":[]},{"id":"234672ff.22406e","type":"queue config","z":"","name":"","storage":"fs","path":"safe-queue-folder","timeoutAck":"1000","startJob":true,"typeTimeout":"retry-times","typeError":"move-error","retryTimeout":"3","retryError":"","maxInMemory":""},{"id":"4509155d.f4762c","type":"mqtt-broker","z":"","name":"","broker":"lager","port":"1883","clientid":"","usetls":false,"compatmode":false,"keepalive":"60","cleansession":true,"birthTopic":"","birthQos":"0","birthPayload":"","closeTopic":"","closeQos":"0","closePayload":"","willTopic":"","willQos":"0","willPayload":""}]
At the server side you should do something like this to send the ack back
[{"id":"11e4c166.e87c2f","type":"tab","label":"Server","disabled":false,"info":""},{"id":"612bc0e5.357b7","type":"mqtt in","z":"11e4c166.e87c2f","name":"","topic":"data","qos":"2","datatype":"json","broker":"4509155d.f4762c","x":150,"y":200,"wires":[["ef5aa389.1bc04","9d9bcc6c.00c7a"]]},{"id":"ef5aa389.1bc04","type":"change","z":"11e4c166.e87c2f","name":"Prepare ack","rules":[{"t":"set","p":"payload","pt":"msg","to":"payload.ack","tot":"msg"}],"action":"","property":"","from":"","to":"","reg":false,"x":350,"y":240,"wires":[["668140dd.194ae"]]},{"id":"668140dd.194ae","type":"mqtt out","z":"11e4c166.e87c2f","name":"","topic":"data/ack","qos":"","retain":"","broker":"4509155d.f4762c","x":550,"y":240,"wires":[]},{"id":"794ac09f.7d142","type":"comment","z":"11e4c166.e87c2f","name":"send ack back to the clients","info":"","x":780,"y":240,"wires":[]},{"id":"bfd11dd7.83529","type":"comment","z":"11e4c166.e87c2f","name":"Treat the data in the server","info":"","x":770,"y":160,"wires":[]},{"id":"9d9bcc6c.00c7a","type":"change","z":"11e4c166.e87c2f","name":"Manipulate data","rules":[],"action":"","property":"","from":"","to":"","reg":false,"x":360,"y":160,"wires":[[]]},{"id":"4509155d.f4762c","type":"mqtt-broker","z":"","name":"","broker":"lager","port":"1883","clientid":"","usetls":false,"compatmode":false,"keepalive":"60","cleansession":true,"birthTopic":"","birthQos":"0","birthPayload":"","closeTopic":"","closeQos":"0","closePayload":"","willTopic":"","willQos":"0","willPayload":""}]