For a start you have a syntax error, which the error console would confirm.
lightbox.trigger('.fslightbox-slide-btn-container-next"'); //<-- "
Secondly, you seem to be making considerable assumptions on what
trigger() does and how it works, believing that you pass it a selector and it triggers a click event. That’s not how it works. I think you mean:
CLICK HERE to find out more related problems solutions.