While there is an option to have a terms and conditions page presented to users when they register - Configuring Terms and Conditions - the ability to present a users with a pop-up each time the post content is not available in the out of the box option. As such there are a few options available to you if you are interested in this type of feature.
1. If you are waiting to see this as an option in a future release I would suggest creating an idea in the Ideas for Jive space where out Product Managers review through top rated ideas when considering new features.
2. If you are interested in adding a custom feature into your instance our Professional Services team can assist in determining the scope of the project and work with you to develop a solution which meets your needs. If you are interested in this option please submit a case in your customer group here in the Jive Community and the next available support engineer can get this process started for you.