This should help you on your way
Fill in the url of the api endpoint and provide the api key.
Providing the actual query needs to be done via template or function node.
example flow:
[{"id":"a617e6cd8e2621bd","type":"inject","z":"76cc522bcab02e02","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"","payloadType":"date","x":360,"y":1540,"wires":[["f445212f3b945c9f"]]},{"id":"59c2306d202e87a5","type":"debug","z":"76cc522bcab02e02","name":"debug 596","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":910,"y":1540,"wires":[]},{"id":"f445212f3b945c9f","type":"function","z":"76cc522bcab02e02","name":"graphql query","func":"const query = `\n{ boards (limit:1) {\n name\n id\n description\n items {\n name\n column_values {\n title\n id\n type\n text\n} } } }\n`\n\nmsg.payload = {query}\nreturn msg;","outputs":1,"timeout":0,"noerr":0,"initialize":"","finalize":"","libs":[],"x":520,"y":1540,"wires":[["4c33692c0ea99d38"]]},{"id":"4c33692c0ea99d38","type":"http request","z":"76cc522bcab02e02","name":"","method":"POST","ret":"txt","paytoqs":"ignore","url":"","tls":"","persist":false,"proxy":"","insecureHTTPParser":false,"authType":"","senderr":false,"headers":[{"keyType":"Content-Type","keyValue":"","valueType":"application/json","valueValue":""},{"keyType":"Authorization","keyValue":"","valueType":"other","valueValue":""}],"x":710,"y":1540,"wires":[["59c2306d202e87a5"]]}]