I want to add a visual effect at the end of one of my functions but I don’t know how to reference a niagara component that’s inside a blueprint class, is that currently possible? Thanks! 
It’s not yet possible unfortunately.
You could move the niagara effect to a new single blueprint prop or attach it to an empty prop. Make it loop then hide it from sight and use the TeleportTo function to make it visible again (for a short amount of time if you want)
You’ll loose the anticipation and death part of your niagara effect since you have to make it loop for this to work.
Prop manipulators won’t work since they introduce visual lag (sort of update collisions first) and they won’t activate the niagara effect, but you may try.
We need niagra parameter collections for this to work. Basically similar to how we can create and update material parameter collections via the sequencer, we need the same for niagra. Not sure why it’s not exposed in UEFN yet.