Fathers rights, can my child's mother have him circumcised without my agreement?

I'm not circumcised and I could kick my father's butt for taking the same position you're taking. Since she's the child's mother and since the two of you have split, my guess is you have no legal grounds for derailing her intentions. But, in fairness to you - let me say I'd call a divorce atty and ask. It's a simple question with rather cut and dry circumstances - you should be able to get the answer on the phone.