From the manual:
Working with Objects
To select a part of the displayed values in for example a bar chart, or to select multiple lines in a line chart, hold your finger on the object until the resizable selection area pops up. Resize the selection area according to your preference, and press the Select button at the top left-hand corner. The selected values are now displayed.
This appears to be what is happening, but my charts are read-only. Shouldn't that make selections impossible?
Orientation and Zooming
Rotating the small device 90° allows working with the QlikView document in landscape orientation.
Zooming of QlikView objects is supported when having opened the document in full browser version, using the regular zooming functionality of the small device.
That's all there is on zooming in the manual.