Q.What Is The Circle Of Black Spots That Is Growing On The Underside Of The Leaves On My Stocks
they are in a pot with other flowers and all are doing well, including the stocks.

Certified GKH Gardening Expert
Unfortunately, your photo did not come through. I am unable to ID the problem. Normally, black spots will be bacterial, or fungal. This will signify that the soil does not get a chance to dry out thoroughly between waterings.
Here are some articles to help:
https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm
https://www.gardeningknowhow.com/garden-how-to/info/applying-bactericide-to-plants.htm
https://www.gardeningknowhow.com/ornamental/flowers/stock/growing-stock-flowers.htm