Check the documentation for mysqlimport at http://www.mysql.com/doc/en/mysqlimport.html
There are numerous switches that may be applicable
Those two may be the most applicable.
Verbose mode. Print out more information what the program does.
Most warnings will occur for rows where you attempt to insert null values into columns defined as not null... or where the data for a column exceeds the length of the datatype defined for that column... and finally for incorrect datatypes (e.g. string into date column).
One idea is to dump the table into a text file of precisely the same format and then perform a diff (http://www.textpad.com/ is a good win32 tool for large diffs) to determine the rows that have errors. Most likely you'll find a few columns were truncated because of insufficent;y size datatypes for the values you were inserting.
Ignore that crap... just looked through the MySql documentation some more... and it seems that this page has the answer for you: http://www.mysql.com/doc/en/SHOW_WARNINGS.html