Two of those will almost certainly be ground and power supply - you could start by tracing those two first.
Then once you have those, look around in the datasheet for the proper supply voltage. From the looks of it I would guess 5V - but better not risk it; just look it up from datasheets.
Once you have that, you can apply power to the board.
Then put a 10k resistor in series with an amp meter (you risk destroying the board and/or your power supply without this resistor), and check each pin against ground and power, to see whether the keyboard pulls any of the pins to ground or power.
If you are certain it is an AT protocol keyboard, look up the AT protocol. The sources I find say the keyboard sends a self-test status code shortly after getting powered on, even without a computer being connected.
So you could take a scope, and look at the other pins during powerup, to see where it sends that out. Looking here:
http://www.hardwarebook.info/AT_Keyboard/Mouse_protocol one line - the clock - should send about a dozen regular pulses, while the other line - data - would contain the actual bits of the data
(BAT code) so it would not just be regular pulses.
Aimed with this information, all that remains for you is to wire up a cable with the determined pinout.
Assuming your information about this being an AT protocol keyboard being right.
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