Why might my cordyline have these yellow and brown spots?
Spots on Leaves
Certified GKH Gardening Expert
That appears to be the start of a fungal infection. Wettable sulfur will kill of anything in the soil, and dolomitic lime will help to keep the pH stable while this is taking place.
Here is an article that will give you more information on the care of these: https://www.gardeningknowhow.com/houseplants/ti-plant/growing-hawaiian-ti-plant-indoors.htm