If the parent is invited to the conference, he should be seeing it in the 

* Sign ups tab (All groups / class page)
* Notification center (bell icon) on the top right
* He will also see a Post in the Home feed. 

If he is not seeing it anywhere, then he is not invited. The teacher needs to check her conference schedule and see if that parent is invited or not. If not, she needs to invite him/her. 

To invite the parent to the conference that is already created: 

* Click on the conference
* Click Options
* Click Invite More People
* Click the parent 
* Click Next
* Click Send.