Answer:
You can not join Turkish Army if you are not a citizen of Republic of Turkey.
If you are a male Turkish citizen, you are subject to draft, regardless of your ethnic origins. So you will join the armed forces, anyway.
Things get a little complicated if you want to be an officer in Turkish armed forces, but you are not an ethnic Turk. The armed forced intelligence does a extensive background check to allow you in. I have not heard a single case like that.
However Pakistani nationals are trained Turkish armed forces academies, if they are sent there by Pakistani armed forces.