This depends n how your divorce decree and/or parenting plan is written. If you have 'joint decision making' written into the parenting plan then you do have some input as to whether or not the child is homeschooled. Be aware that even with joint decision making in the parenting plan, the custodial parent's wishes will often prevail in court unless you can present compelling reasons as to why the child shouldn't be homeschooled.
If you don't have 'joint decision making' specified in the parenting plan and you are not the custodial parent, then you may not have any legal authority to determine the child's educational environment. You are, however, still entitled to complete access to your child's school records, unless specifically disallowed in the parenting plan.