Like it says. Will the game run on this hardware? And how well?
OS: Mac OS X 10.10.1 (Yosemite)
Processor: 2 GHz Intel Core 2 Duo
Memory: 8 GB 1067 MHz DDR3
Graphics: NVIDIA GeForce 9400 256 MB
Display: 20-inch 1680x1050

According to the minimum requirements listed by GOG.com it doesn't. Your processor as well as your graphics card are too weak, especially as the game is known to perform worse on Mac compared to Windows.
It might still run, but you have to expect lags and the necessity to decrease your resolution as well as quality settings. Further GOG support won't be much of a help, as they'll say you don't meet the minimum requirements.

Unfortunately, I think there's no demo for the Mac version to try it first hand.

In windows you would possibly get a message saying "Minimum requirement not met" but there is a workaround for this by adding a line in the shortcut's properties. I doubt the same workaround would be done in mac so my guess is that you'll have problems with so little VRAM.

I guess there is only one way to find out; you can wait for the next sales so you can buy Witcher EE with a -90% discount (around $1). That way, even if you won't be able to run the game, you won't lose too much money! ;-)

Cheers!

You really don't want to even try it on that spec. I tried to play the Win version of this on a 2009 13" MacBook Pro with a similarish spec to yours:

2.53Ghz, 8GB Ram, SSD, 13" Screen at 1280x800, Nvidia 9400m 256mb but in Bootcamp (Probably WinXP at the time, could have been Win 7)

The results where not good, even at the lowest possible detail settings I was getting periods of 1-2FPS. Basically it along with games like LA Noire, Ghostbusters and others went into a "Unplayable on 2009 MBP" category.

That said on the same computer I did 130 hours of Dragon Age Origins and 60 hours of Divinity Original Sin at roughly ~10-14 FPS. Both at the lowest settings possible (apart from screen res).

Having just got a new computer I'm about to download TWEE 1 myself so I can finally play it :)