Use:

this.videoCaption.subtitlesEl.on({
    'scroll': this.videoCaption.autoShowCaptions,
    'scroll':  this.videoControl.showControls
});

or chaining:

this.videoCaption.subtitlesEl
            .on(
                'scroll',
                this.videoCaption.autoShowCaptions
            ).on(
                'scroll',
                this.videoControl.showControls
            );

I prefer the first form, it is clearer.