If I leave my current job what commissions am I entitled to when I depart?

There is no general answer in the law to this, because the law does not address entitlement to commissions. Rather, the answer is found in the terms of the agreement (whether written or unwritten) under which you worked for commissions, since it is equally legal that you get commissions from all sales even if you leave employment or that you must be employed at the time commissions are actually paid out to receive them--it all comes down to what you and the company agreed to.
Obviously, if there is a written commission, etc. agreement, you look to its terms first--if there is such an agreement and it address this issue, its terms control. If no contract, look to any employee or sales manual or other non-contractual writing from the employer which touched on this issue: they can be used as evidence of what the understanding or agreement was. If nothing like that, look to past practice: where other reps paid in the past when they left employment? What has been done in the past is a guide to the understanding and agreement. If there is NOTHING showing what the understanding about commission payment is, then look to the industry norms--what is done at other companies in your field. If the matter went before a court, if all else failed, the court would typically look at industry norms to see what the parties, in the context of their industry, most likely intended and understood.