can i use this product to attach brick veneer to cinder block? Also, will it slide down without any support or does it hold pretty quickly?

Yes, The Loctite Power grab Ultimate White can be used for this application depending on the scope of the project. However, keep in mind this product is not a thinset adhesive nor should it be considered as a replacement to thinset or mortar where one is required. If this is a major project as in a complete or full wall system, it is recommended you consult the brick veneer manufacturers specific installation instructions and recommendations.