Hi,
If you follow the code the ' movf d1,w ' this moves the data held in d1 into W to be passed to the TX REG for transmission, so your data is already there, saved.
So when, I assume, the data from the gps module is stored in d1, then thats the time to write it to eeprom.
You have some eeprom on the 877A chip but for large amounts of data you have to use the external eeprom you mention though it uses a different serial protocol to the serial RS232.
The Pic chip has an SPI serial protocol but I do not know if that is exactly compatible with the ATmel eeprom chip ? - perhaps your tutor is testing you there ?