How should a 1098 for co-owned home be split after divorce?

It depends. ‌If you and your ex-spouse agreed to split the interest, then yes.‌ You can each enter half of the interest. ‌It does not have to be exactly half, as long as the total between the 2 of you equals the total amount on the 1098, that is acceptable. 

When you enter your portion of the interest from the 1098 into TurboTax Online, check the box that says "the interest amount I entered is different than what's on my 1098."

If you can, you should split the expenses based on who paid what portion.  For example, if you jointly paid until June and then only spouse A paid the rest of the year because only spouse A paid the mortgage, then it would be about 3/4 spouse A and 1/4 spouse B.