TestCellWithLocation.swift

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell: CustomCell = CustomCell()
    cell.button.addTarget(self, action: #selector(buttonClicked(sender:)), for: .touchUpInside)
}

func buttonClicked(sender: UIButton) {
    let tapLocation = sender.convert(CGPoint.zero, to: tableView) //取得按鈕位置
    let tapIndexPath = self.tableView.indexPathForRow(at: tapLocation) //這個位置位於哪個indexPath
    print(tapIndexPath.row)
}