I was able to activate this option once in my MacOS intellij version, but could never find this option anymore, I forgot its name.
I know there is the CTRL+SHIFT+P alter
Adding to @Simulant and @zero answers
In the latest version of IntelliJ (2020.3) you need to go to Settings -> Editor -> Inlay Hints where you can specify "Show hints for" (for specific language) and then in Settings -> Editor -> Inlay Hints -> Kotlin -> Parameter hints -> Types you can specify what type of hints you want.