Or if you want two separate message payloads on different wires
[{"id":"2b1db6cff0ff0516","type":"inject","z":"613df62afc8a16bf","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"dining/dht1","payload":"{\"temperature\": 42, \"humidity\": 90}","payloadType":"json","x":250,"y":120,"wires":[["ed1d294022b465ed"]]},{"id":"ed1d294022b465ed","type":"split","z":"613df62afc8a16bf","name":"","splt":"\\n","spltType":"str","arraySplt":1,"arraySpltType":"len","stream":false,"addname":"","property":"payload","x":370,"y":120,"wires":[["20d40bc84d811fdd"]]},{"id":"20d40bc84d811fdd","type":"switch","z":"613df62afc8a16bf","name":"","property":"parts.key","propertyType":"msg","rules":[{"t":"eq","v":"humidity","vt":"str"},{"t":"eq","v":"temperature","vt":"str"}],"checkall":"true","repair":false,"outputs":2,"x":510,"y":120,"wires":[["e3d2e85561651a6a"],["eed0e334329a42d4"]]},{"id":"e3d2e85561651a6a","type":"debug","z":"613df62afc8a16bf","name":"humidity","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"payload","targetType":"msg","statusVal":"","statusType":"auto","x":660,"y":100,"wires":[]},{"id":"eed0e334329a42d4","type":"debug","z":"613df62afc8a16bf","name":"temperature","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"payload","targetType":"msg","statusVal":"","statusType":"auto","x":670,"y":140,"wires":[]}]
You can also copy the keys to msg.topic (or any other property) in the split node if required.