So I have to make a cladogram for a school project and I'm really having trouble.?

A cladogram is just a tree of shared characteristics. Ideally all items on a branch should share a common characteristic which other items don't have. So you could have say
burrowing/non-burrowing, carnivore/herbivore, horns/hornless.

What's a cladogram?

the nyalla and gazelle are more closely related to each other than they are to the bison. All 3 are artiodactyls, or even toed ungulates. the rhino and the zebra are closest relatives to each other among these 8 as they are perissodactyls or odd-toed ungulates. The wild dog and the lion are closest relatives, because they are both members of the Carnivora. The aardvark is the odd one out as the other 7 are more closely related to each other than they are to the aardvark. I am not sure about the relationships between artiodactyls, perissodactyls and carnivores but I think artiodactyls are probably more closely related to carnivores than to perissodactyls. Others may disagree but that is science, as there is often disagreements, especially when dealing with evolutionary relationships, since the past cannot be observed directly, but must be inferred using the available evidence.