The total number of subscribers to your show is displayed near your show name on the landing page for your show.
Click the New subscribers tab to see a chart of subscription activity during the selected time period. The value shown on the New subscribers tab is the net change in subscribers from the beginning to the end of the selected time period.
What's that dip?
If you see a perfectly symmetrical dip in your subscriber data with a net change of (about) zero subscribers, this probably means that the served feed changed during that period. When this happens, you "lose" subscribers from your old feed to your new feed; after you verify ownership of the new feed, you "gain" all the lost subscribers. When this happens, you don't need to worry or do anything; it's just an accounting blip.