Find files modified today, using command line (bash)
There are several ways to do this in bash from the terminal - depending on exactly what you want to find:

Find files modified in the last 24 hours

find / -mtime -1 -print


Find files modified today (likely what you want)

find / -newerct 'yesterday' -print


or, using Spotlight

mdfind date:today


This can also be done from the GUI with Spotlight.


Open Spotlight (option-command space by default).
Add a criteria to search for, by hitting the Plus sign near the top
right of the Spotlight window.
Change the criteria to "Last modified date" is "today."