Double-tap Esc when editing a page containing ACF-fields, to easily inspect ACF field names and keys.
First of all, you have to be logged in as an administrator. The plugin is simply not enabled for other roles.
Then, once on a content page, simply double-tap the Esc-button to enable the visual aid. For each ACF-field, you should now see the field name and field key displays along with the label.
If you click a field name or key, it will copy the value to your clipboard (requires Adobe Flash-plugin enabled in your browser).
See the screenshots. It should be pretty self explainatory.