Bar selection is equivalent to data point selection, and as such there are delegate methods which you can implement to be notified of selection events.
You need to choose the selection mode on the series as series or point (sounds like you want point selection):
barSeries.selectionMode = SChartSelectionPoint;
And then implement the following delegate method:
- (void)sChart:(ShinobiChart *)chart toggledSelectionForPoint:(SChartDataPoint *)dataPoint inSeries:(SChartSeries *)series atPixelCoordinate:(CGPoint)pixelPoint
That method will be called as users select and deselect points.