ExpediaGroup’s set of libraries is the most popular toolkit for running GraphQL in Kotlin
https://github.com/ExpediaGroup/graphql-kotlin
There are some good examples provided. One of them is using Spark Framework for serving data. It can be a good starting point for a small project
https://github.com/ExpediaGroup/graphql-kotlin/tree/master/examples/spark
According to the Spark website, it positions itself as an alternative to NodeJS/TypeScript world.