If the Do not display this message again checkbox is marked to turn off the Mass Transaction Entry window prompt as shown below, there is not a window option to turn this back on. You can run this SQL script in Management Studio on the company database. Note that the script below will reset the flag for all users. If you would like to restrict to a certain user, add where USERID = 'enter users login id'. A zero value turns off the prompt a value of 1 turns on the prompt.
update SY01401 set USRDFSTR='0' where coDefaultType = '16' --DOES NOT receive prompt
update SY01401 set USRDFSTR='1' where coDefaultType = '16' --DOES receive prompt