What do you mean by "select"? Are you intending to evidence them while for example drawing a line across the set of measures? If so, plot functions like for example PlotXY have options to evidence single points with various symbols. On the other hand, if you want to point on the graph and obtain the values of a single measure you can do it using cursors: you can enable one or more cursors on the graph and interactively select a point on the graph; in the graph callback you can retrieve cursor values and either display measures on numeric indicators or handle them according to your needs. Have a look of the examples shipped with CVI: you can retrieve them in the example finder or looking at <cvidir>\samples\userint folder.
