According to Adobe's help site:
Select the anchor points. If they are not visible, use the direct selection tool to view the points. Selecting the lasso tool will allow you to enclose a collection of points. Clicking on a point, shift clicking on additional points is the more manual method of selecting multiple points, other methods may be available.
Once selected, two icons on the tool bar become useful and effective. One of them is the "convert to corner point" icon, while the other is "convert to smooth point." If you pause your mouse over the icon, a tool tip may appear with these identifiers.
The above text is paraphrased from the linked site which also contains images of the icons used in the process.
I tested this process on an .SVG file that was converted to .AI which worked for some of the anchor points. This may be an artifact of the original file format, or the process may work only on some anchor points. Experimentation is indicated.
Inkscape works in a similar manner, although you can select a point when using the node editing tool, pausing your mouse over the point and scrolling the mouse wheel. This will advance the number of selected anchor points (nodes) being selected. Alternatively, one can also rubber-band a box around the desired points.
A similar reference for Inkscape can be found at tutorviacomputer.com for node editing. The difference in action is once the nodes are selected, use Shift-C to convert to corner nodes. The text also provides the option to use the "make selected nodes corner" icon.