You forgot the backticks around the keys.
Example flow:
[{"id":"29831854.f21a78","type":"inject","z":"97f8fffc.342b1","name":"","topic":"","payload":"{ \"weatherdata\": { \"-xmlns:xsi\": \"http://www.w3.org/2001/XMLSchema-instance\", \"product\": { \"-class\": \"uvforecast\", \"time\": { \"-to\": \"2019-07-09T12:00:00Z\", \"-from\": \"2019-07-09T12:00:00Z\", \"location\": [ { \"-altitude\": \"0.00\", \"-longitude\": \"11.00\", \"-latitude\": \"56.75\", \"uv\": { \"uvi_clear\": { \"-value\": \"5.21\", \"-unit\": \"uv-index\" }, \"uvi_partly_cloudy\": { \"-value\": \"4.43\", \"-unit\": \"uv-index\" }, \"uvi_cloudy\": { \"-value\": \"1.35\", \"-unit\": \"uv-index\" }, \"uvi_forecast\": { \"-value\": \"5.18\", \"-unit\": \"uv-index\" }, \"ozon\": { \"-value\": \"7.755525e-03\", \"-unit\": \"kg/m^-2\" }, \"snowcover\": { \"-value\": \"0.00\", \"-unit\": \"percentage\" }, \"cloud_cover\": { \"-value\": \"1.00\", \"-unit\": \"parts of 8\" }, \"albedo\": { \"-value\": \"0.05\", \"-unit\": \"percentage\" }, \"solar_zenith\": { \"-value\": \"34.41\", \"-unit\": \"angle\" } } }, { \"-altitude\": \"0.19\", \"-longitude\": \"29.00\", \"-latitude\": \"64.00\", \"uv\": { \"uvi_clear\": { \"-value\": \"4.51\", \"-unit\": \"uv-index\" }, \"uvi_partly_cloudy\": { \"-value\": \"3.83\", \"-unit\": \"uv-index\" }, \"uvi_cloudy\": { \"-value\": \"1.17\", \"-unit\": \"uv-index\" }, \"uvi_forecast\": { \"-value\": \"1.17\", \"-unit\": \"uv-index\" }, \"ozon\": { \"-value\": \"7.077940e-03\", \"-unit\": \"kg/m^-2\" }, \"snowcover\": { \"-value\": \"0.00\", \"-unit\": \"percentage\" }, \"cloud_cover\": { \"-value\": \"8.00\", \"-unit\": \"parts of 8\" }, \"albedo\": { \"-value\": \"0.05\", \"-unit\": \"percentage\" }, \"solar_zenith\": { \"-value\": \"41.66\", \"-unit\": \"angle\" } } }, { \"-altitude\": \"0.32\", \"-longitude\": \"22.25\", \"-latitude\": \"67.75\", \"uv\": { \"uvi_clear\": { \"-value\": \"4.10\", \"-unit\": \"uv-index\" }, \"uvi_partly_cloudy\": { \"-value\": \"3.49\", \"-unit\": \"uv-index\" }, \"uvi_cloudy\": { \"-value\": \"1.07\", \"-unit\": \"uv-index\" }, \"uvi_forecast\": { \"-value\": \"3.07\", \"-unit\": \"uv-index\" }, \"ozon\": { \"-value\": \"6.717272e-03\", \"-unit\": \"kg/m^-2\" }, \"snowcover\": { \"-value\": \"0.00\", \"-unit\": \"percentage\" }, \"cloud_cover\": { \"-value\": \"5.00\", \"-unit\": \"parts of 8\" }, \"albedo\": { \"-value\": \"0.05\", \"-unit\": \"percentage\" }, \"solar_zenith\": { \"-value\": \"45.40\", \"-unit\": \"angle\" } } } ] } } } }","payloadType":"json","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":315,"y":200,"wires":[["9d120015.e2b778"]]},{"id":"d1a1d270.68b8f","type":"debug","z":"97f8fffc.342b1","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","x":670,"y":200,"wires":[]},{"id":"9d120015.e2b778","type":"change","z":"97f8fffc.342b1","name":"","rules":[{"t":"set","p":"payload","pt":"msg","to":"payload.**.location[`-longitude`='11.00' and `-latitude`='56.75'].**.uvi_forecast","tot":"jsonata"}],"action":"","property":"","from":"","to":"","reg":false,"x":480,"y":200,"wires":[["d1a1d270.68b8f"]]}]
