Would the Seljuqs have looked "Asian" like modern Mongolian people? If they were descended from Khazars from Ukraine, would they have looked like Russian people?
Because they ruled a lot of the Middle East and Persia, would they be tan "ethnic" white people like modern people in Turkey and Iran?
Seljuks aren't the descendants of Khazars, and Khazars probably didn't look a lot Slavic, as they were a Turkic people as well.
Depictions of Seljuk rulers, Alp Arslan in particular, usually show both them and their soldiers having Mongoloid features.
The very fist Seljuqs, including Tughril, would most likely have appeared somewhat East-Asian and somewhat Middle-Easter, like many in modern day Kazakhstan and Turkmenistan, as they came from central Asia. After a generation or two, however, they would have began to look more like modern day Iranians and Turks, as their empire was centered in Iran. By the third ruler of the Seljuq Empire, for example, they bagan adopting Iranian names and titles.