Your sentence is almost correct! Here's a good way to write it:
"Reindeer have a great sense of smell. They can find lichen even under the snow."
The sentence you provided is perfect as it is! It correctly talks about reindeer having a strong sense of smell and their ability to find lichen beneath the snow. If you want, you can combine the two sentences with 'and':
"Reindeer have a great sense of smell, and they can find lichen even under the snow."
Great job!