To see your mobile rankings on Rank Tracker, you must first have an Advanced or Agency plan:
Then, head to Rank Tracker and select one of your projects. Click "Mobile View":
In this report, you'll be able to see all your mobile rankings for the keywords you're currently tracking. You'll be able to see their positions, whether they rank for any particular mobile SERP features and tons of other information.
Do note that your Rank Tracker needs to be set up, i.e you're already tracking keywords in Rank Tracker.