Ctrl as primary modifier. The Google Docs shortcut set on ChromeOS uses Ctrl, matching the Windows version. If you've used Google Docs on Windows, the same Ctrl-based shortcuts apply on ChromeOS.
The Search/Launcher key. Chromebooks replace the standard Caps Lock key with a Search key (also called the Launcher key, it looks like a circle or magnifying glass). This key is used in several ChromeOS system shortcuts. Within Google Docs, it rarely appears in Docs-specific shortcuts, but it's worth knowing it occupies the Caps Lock position if you're looking for that key.
Chromebook keyboard and F-keys. Standard Chromebook keyboards don't have traditional F-key rows. The top row serves as function keys (screen brightness, volume, refresh, etc.), and accessing them as F-keys requires holding Search+top-row-key. Google Docs shortcuts that might use F-keys on Windows behave differently on ChromeOS. The table above covers what applies on ChromeOS specifically.
Built-in shortcut list. Ctrl+/ opens Google Docs' built-in shortcut reference panel on ChromeOS, the same as on Windows. This is the fastest way to find a Docs shortcut without leaving the document.
Heading styles. Ctrl+Alt+1/2/3 applies Heading 1/2/3 in Google Docs on ChromeOS, matching Windows exactly.
Suggesting mode and comments. Both work on ChromeOS with the same Ctrl-based shortcuts as on Windows. Suggesting mode, Google Docs' tracked-changes equivalent, is fully supported on Chromebook.