How do I file a dependents social security benefit?

[LinaJ2018]

If the social security benefit is issued in your dependent's name, you do not report it on your tax return. 

If the social security benefit is the only income your dependent receives during the year, he or she is not required to file a tax return.  If your dependent receives income other than the social security, he or she is required to file if meets the filing requirements.  Please see 2018 Filing Requirements

[VolvoGirl]

You don’t.  It only goes on their return.  If that is the only income they have they do not have to file a return and nobody reports it.