How to find command by pressing keybinding in VSCode

You can find the command associated with a key binding by typing the keybinding into the Keyboard Shortcuts search box:

Unfortunately, per the source code, the vim extension doesn't use this mechanism to bind the o key.

Fortunately, it does let you rebind the keys in settings. First, open settings (F1 Preferences: Open Settings), then add (to bind i, for example):

"vim.normalModeKeyBindingsNonRecursive": [
    "before": ["i"],
    "after": ["o"]
],

If you have the new settings UI, you might need to search for vim.normalModeKeyBindingsNonRecursive first, and then click Edit in settings.json.

As of the September 2018 release, VSCode can do this from the keyboard shortcuts window.

From the keyboard shortcuts window (cmd+k cmd+s), type cmd+option+k or click the keyboard icon on the right.

Kudos to this comment linking to this approach as an answer to another question.