Had to do this recently. You need to use [tableView rectForRowAtIndexPath]
.
However, one of the things that can catch you out is that as you scroll through the UITableView you need to take account of the offset (ie something reporting its y position as 3000 pixels is of course meaning 3000 from the top of the UITableView - not 3000 pixels on the screen).
In addition to this, it will naturally appear at the top of the cell, so you need to add half the height of the cell to the calculations.
This code worked well for me:
CGRect frame = [tableView rectForRowAtIndexPath:indexPath];
CGPoint yOffset = self.tableView.contentOffset;
[self.popoverController presentPopoverFromRect:CGRectMake(frame.origin.x, (frame.origin.y + 45 - yOffset.y), frame.size.width, frame.size.height)
In my case each cell was 90 pixels high, hence the '+45' bit. Substitute half your own cell height.