Most hotkeys are customizable in Obsidian.
We only defined default hotkeys for the most commonly used commands, but if you frequently use a command, it would save you lots of time if you add a hotkey for it.
For a list of default hotkeys, see here.
The fastest way to see the hotkey set for a command is to find the command in Command palette. If there's a hotkey listed for that command, it's set.
To add a hotkey, remove a hotkey, or restore hotkeys to default, go to Settings => Hotkeys. Note that you can also filter the list, as the list of commands is quite long.