These versions of Outlook don’t use .nk2 files anymore. The cached emails are saved in:

%LOCALAPPDATA%\Microsoft\Outlook\RoamCache (which is C:\Users\<username>\AppData\Local\Microsoft\Outlook\RoamCache)

And the actual file is called: Stream_AutoComplete_0_{GUID}.dat

I had to do this because of a migration to Office 365. To copy (migrate) the information on this file to a new Outlook Profile:

• Identify which one is your current file linked to your main Outlook profile and make a copy of it as a safety measure (check its modified date/time to identify it).
• After configuring your new Outlook profile, send an email so it will create its new AutoComplete file after Outlook is closed. Identify this file.
• Copy the name of the new created file, delete it and rename the old AutoComplete file using the new name.