Is that just in a scripting block in the event sheet? Can you give more context? When I try it in a scripting block, I don't get that parsing error marking. Ashley has noted in the past that script blocks are default inside async functions, so you can use await in event scripting.
Ah, if you are doing it in just a separate C3 JS script file, you need to make the function calling the below function async also, for example:
async function readJSONFile() {
const jsonData = await runtime.callFunction("readJsonFile")
console.log('jsonData:', jsonData)
}