If I would like to know whether a binary can be run from the command line, X Window System or both, how do I tell without access to the Internet?
However, it does not mean it requires X11; this is impossible to determine programmatically without either examining source code or running the program. For example, a program may display a graphical window if X11 is available, and a text interface otherwise.
If the executable is statically-linked, run
Read the man page.
Though you may actually have to read the fool thing rather than glancing at the usage and quickly paging through the options.