Q: How to access another iPhoto library on a shared MacBook Pro ?

Access from where, another user account? The only way to share a library from two user accounts on a Mac is to have the library on an external HD that is formatted OS X Extended (journaled) with ownership set to be ignored.

See this Apple document for more details: iPhoto: Sharing libraries among multiple users - Apple Support

Rossky wrote:

 

Access from another user account. Two user accounts on a Mac ...

Get an external HD as I mentioned.

Make sure the drive is formatted Mac OS Extended (Journaled)

1. Quit iPhoto

2. Copy the iPhoto Library from your Pictures Folder to the External Disk.

3. Hold down the option (or alt) key while launching iPhoto. From the resulting menu select 'Choose Library' and navigate to the new location. From that point on this will be the default location of your library.

4. Test the library and when you're sure all is well, trash the one on your internal HD to free up space.

Regards

TD