The location of the NK2 AutoCompelete file created by Outlook might be different from one computer to another, depending on the operating system and the version of Outlook.
Here's the rules for finding the location of your NK2 file:

• For Outlook 2003/2007 with Windows 2000, Windows XP, or Windows Server 2003:

The location of the nk2 file is

 C:\Documents and Settings\[User Profile]\Application Data\Microsoft\Outlook

The name of the NK2 file is identical to the Outlook profile name, with .nk2 extension.

• For Outlook 2003/2007 with Windows Vista, Windows 7, or Windows server 2008:

The location of the nk2 file is

 %USERPROFILE%\AppData\Roaming\Microsoft\Outlook

The name of the NK2 file is identical to the Outlook profile name, with .nk2 extension.

• For Outlook 2010/2013 with Windows Vista, Windows 7, or Windows server 2008:

The nk2 file is located in

 %USERPROFILE%\AppData\Local\Microsoft\Outlook\RoamCache

The name of the NK2 file is in the following format:

Stream_Autocomplete_X_AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA.dat

The X is the file index (usually 0) and AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA is a random 16-byte key in hexadecimal format.

* For Outlook 2010/2013 with Windows XP: The nk2 file is located in

C:\Documents and Settings\[User Profile]\Local Settings\Application Data\Microsoft\Outlook\RoamCache

The name of the NK2 file is in the following format:

Stream_Autocomplete_X_AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA.dat

The X is the file index (usually 0) and AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA is a random 16-byte key in hexadecimal format.