Missing Cotyledon

DO NOT spray a seedling this size with anything, it wold be like applying napalm. Your seedling will grow normally, cotyledons are not really needed by the plant, they are not true leaves, their only function is to protect the growing tip as it pushes through the soil to the surface. Just be thankful that your entire plant was not eaten. Damage like this is often caused by cats or birds and not insects, if this occurred during the day, meaning spraying with neem is pointless. Neem should be a last resort and is not as safe as some people think. In fact, in my country it is illegal to use neem on any product intended for human consumption. Healthy cannabis plants growing outdoors are generally not affected by insects too much, caterpillars being the main problem and they are easy to remove by hand, making even "preventative" spraying unnecessary too. Hope this helps,.............. Organoman.

It will do fine. I'd give it a little spray, seeing how it's outdoors.

@buzzybee thanks for the response

When my Amnesia Haze Auto sprouted only one cotyledon was health. I had no issues with it growing into a healthy seedling.

If it doesn't get attacked anymore you will be fine. I just lost 4 I started outside. Something ate them. I got some inside I'll put outside when they get a bit bigger.