In Windows, you can use the IDE and click the "index" tab and then the "actions" tab. The "Commands available to the player" section has everything. Things are different for Inform 6G and Inform 6L, though. I cut/pasted the text from each section, so there is a sort of checklist.
https://www.dropbox.com/s/zxupqis1mxq2cpk/6g.txt?dl=0
https://www.dropbox.com/s/vuca4ks7lxvd4ha/6l.txt?dl=0