One of the questions said something about being confused on this. The fifteen dog tags are supposed to tell Zhuge Liang who ambushed the bamboo territory, and how to get these Dog Tags, are to beat fifteen X Soldiers. After you kill them, they drop the tags. Also, at the time, you're on another quest about proving you are not a scout for Cao to Ma Su, by killing twenty X Soldiers also. So that won't be hard. The Cogwheel of Time is near the enemy's territory, but you cannot get it until you kill the Lost Soldiers and get the Letter, once you have that Letter, you give it to Ma.