The command is incomplete. This is just the path to the directory where the executable shell script is located. After "script.sh" there must be the name of the cronjob you want to use (ASA 2 has three right now) and the options.
You can find all available options for the product refresh job at http://docs.getasa2.com/cronjobs_repo_refresh.html#options
I would recommend to refresh more than just once a day, maybe once per hour and set a limit for the amount of products to be reloaded on the cronjob execution. This would be the command:
/public_html/wp-content/plugins/amazon-simple-affiliate/scripts/script.sh Asa2_Module_Repo_Cron_Refresh -lt=3600 –limit=50
"Asa2_Module_Repo_Cron_Refresh" after script.sh is the name of the cronjob you want to run. "-lt=3600" sets the LifeTime filter to 3600 seconds and "–limit=50" set the product limit to 50. So this would reload 50 products per hour. I do not know how many products are in your ASA 2 Repo. If there are 1000, 50 per hour would refresh all products over one day.
If "/public_html" is the root directory of your server instance, the command should be ok. If there are other directories above "/public_html", you should adjust that. Please check if there is a cronjob log on your server. There you can see if the job is running as expected or if there are any errors.