You can configure DBirthdays module (mod_dbirthdays) to get birth dates from the popular community component — JomSocial.
There are two methods to configure the DBirthdays module to get dates from JomSocial.

First way

This method should work with default JomSocial configuration. It don´t need any extra manipulations and knowledge, and good for beginners. But this solution generate more load for database, so it has less performance.

Go to the module configuration page and specify these values for parameters:

• Table Birthdays: #__community_fields_values
• Field "Birthday": value
• Field of Identificator: user_id

• Table Users: #__users
• Field of Identificator: id
• Field "Name": name
• WHERE condition: u.block = 0 AND b.field_id = (SELECT MAX(`id`) FROM #__community_fields WHERE `fieldcode` = 'FIELD_BIRTHDAY')

Second way (recommended)

All parameters for the second method are the same, except WHERE condition.

To build WHERE condition you must to know value of the id field from the #__community_fields table, which describes users´ birth dates. To get this value you must:

• Open your Joomla! site database (for example via phpMyAdmin)
• Browse the table jos_community_fields (jos_ — is the default prefix, in your case it may be different)
• Find the row which describes birth date
• Remember it field id value (for example — 3)
  

Now use this value (3) in the WHERE condition like here:

• WHERE condition: u.block = 0 AND b.field_id = 3