"Коли ти їси уранці?"

«Що» is 'what', «коли» is 'when'.

It makes sense because morning is a period of time. You can eat at 6 am, 7 am, 8 am, 9 am, 10 am, and all these will be «вранці». So, this question is asking when exactly.

Of coures, you can use «що» to ask about the food you eat. But it would be a different question.

"Що ти їж/їсиж вранці?" ('їси" on it's own doesn't make sense.)

In literary Ukrainian, the verb «їсти» is conjugated like this:

• я їм,
• ти їси,
• вона/він/воно їсть,
• ми їмо,
• ви їсте,
• вони їдять.

And «їж» in literary Ukrainian is an imperative, used for requests and orders.