When server-based SharePoint integration is turned on, OneNote integration is listed in Document Management.
Go to Settings > Document Management.
Choose OneNote Integration.

Follow the instructions in the wizard to turn on OneNote integration for selected entities. Choose entities that need a full notebook per record. Only entities that are already enabled for document management are listed. Choose Finish.

You can also enable OneNote integration for an entity from the customization form, as long as document management has been enabled for that entity.

A OneNote notebook is automatically created for a record the first time you select the OneNote tab in the activities area in Microsoft Dynamics 365 (online). Once the dedicated OneNote notebook is created for that Dynamics 365 record, you can view and navigate to that notebook from any Dynamics 365 client.
