>Is there a handy command to display all the TAB characters in a file?
>And for a large file, is there a way I can search it in VIM?
One easy way is ":set list". It also shows other control characters, but
it may be exactly what you need. Turn it off with ":set nolist".
If that doesn't do it, you can do / C-V C-I (slash control-V control-I) to
search for a tab character. If you have highlighting turned on, that will
highlight the blank spaces that contain a tab.