UITableView all registered classes / nibs

UITableView stores information about registered cell classes and nibs in separate dictionaries, which you can get using KVC and private property keys:

NSDictionary *registeredCellClasses = [tableView valueForKey:@"_cellClassDict"];
NSDictionary *registeredNibs = [tableView valueForKey:@"_nibMap"];

Each dictionary stores registered cell reuse identifiers as keys and class names/Nib objects as values.

Swift

let registeredCellClasses = tableView.value(forKey: "_cellClassDict") as? [String:Any]
let registeredNibs = tableView.value(forKey: "_nibMap") as? [String:UINib]