I use fvwm, a pretty configurable window manager. In order to set some styles, in order to make certain apps always appear a certain way or on a certain workspace, you fist need to know the window name or class. I’ve found these two X11 programs to be quite helpful to do this.
By default, when you run the program, it changes your cursor and select and left-click on the window you are investigating.

xwininfo

window information utility for X
I use this to find dimensions and location of windows.

xprop

property displayer for X
I use this to find name and class of windows (the very bottom part of output)

These two programs do have other options and probably other functionality, so this is just a subset of their capabilities, still quite useful.