Do I need to have APA citations (footnotes) on every slide of a power point or do I just list them at the end of the presentation?
I don't think we will find an official rule for this if we search the APA manual, since PowerPoint is not listed in the index.
So, we need to rely on common sense & the spirit of the law.
If you are paraphrasing or directly quoting material in you presentation, then yes, you must acknowledge that fact. It seems reasonable to follow the rules for parenthetical references - see this Library page for for info - http://libguides.css.edu/content.php?pid=61826&sid=454619
Your full citations could then appear in a final slide as a reference list.
I think that should cover your bases.