In the graphing menu, go to:
Menu > Construction > Perpendicular
This is the tool for drawing perpendicular lines. Click once on the x-axis to choose this as the line you wish to create the line perpendicular to. Click again at the point where you want to draw the line (x=2).
The line should automatically snap to the point x=2, but if it does not, or you want to specify the position of the line to a more exact location, go to:
Menu > Actions > Coordinates and Equations
Double click on your perpendicular line to display the coordinates at that point, which should be (2,y)
Now ctrl-click on the coordinate box to change the coordinates.
Type in the x-value of your line and the line will jump to that place.
The TI-Nspire certainly takes a lot of getting used to, and the guidebooks aren't really much help, but once you figure these things out it's a really powerful tool.
The process mentioned above is also really good for drawing asymptotes on a graph. You can change the line type to dashed to make it look like an as
ymptote too.