iOS: How to know reloadData() was completed its task?

Try doing this, it should work:

self.tblTimeEvent.reloadData()
DispatchQueue.main.async(execute: {
    self.tblTimeEvent.scrollToRow(at: self.boldRowPath ?? [0,0], at: .top, animated: true)
})

This will execute the scrollToRow on the main thread, that means after the reloadData is done (because it is on the main thread)

As explained in this answer, the reload of the UITableView happens on the next layout run (usually, when you return control to the run loop).

So, you can schedule your code after the next layout by using the main dispatch queue. In your case:

    func getAllTimeEvent()  {
        self.arrAllTimeEvent = ModelManager.getInstance().getAllTimeEvent(from: self.apportmentDateFrom, to: self.apportmentDateTo)
        self.tblTimeEvent.reloadData()
        DispatchQueue.main.async {
            self.tblTimeEvent.scrollToRow(at: self.boldRowPath ?? [0,0], at: .top, animated: true)
        }
    }

You can also force the layout by manually calling layoutIfNeeded. But this is generally not a good idea (the previous option is the best):

    func getAllTimeEvent()  {
        self.arrAllTimeEvent = ModelManager.getInstance().getAllTimeEvent(from: self.apportmentDateFrom, to: self.apportmentDateTo)
        self.tblTimeEvent.reloadData()
        self.tblTimeEvent.layoutIfNeeded()
        self.tblTimeEvent.scrollToRow(at: self.boldRowPath ?? [0,0], at: .top, animated: true)
    }