Many people with diabetes find that cereals are particularly hard to eat due to their effect on blood sugars.
If you do eat cereal would recommend you use whole fat milk / unsweetened yoghurt to add some fat and maybe slow down the absorption of the carbs.
You can experiment by testing what happens after eating various cereals, by testing 2 hours after eating to see if your sugars are where you want them (ideally < 120). Types of cereal (avoid sweetened ones) and also portion size will affect the outcome. If you still go high regardless of which cereal, then you may need to avoid them.
Alternatively eggs scrambled or prepared in some other way with some veges can be a good and healthy choice, with less impact on blood sugars.
Try oatmeal, plain or with cinnamon and nuts. An artificial sweetener to sweeten things up but use in moderation; Stevia, Stevita, Succralose.
None. Cereals are mostly carbohydrates which then get converted to glucose by your body. All cereals raise blood sugar.