With Level Blueprint. Add to scene TextRenderActor and TriggerVolume.Open Level Blueprint. Select TriggerVolume and in Level Blueprint create OnActorBeginOverlap event for TriggerVolume. From WorldOutliner select and drag and drop TextRenderActor. Its create a TextRenderActor reference variable. Drag from pin of TextRenderActor and create Toggle Visibility for TextRenderActor target.
With Actor Blueprint. Create new Actor Blueprint. Add Scene component for Root. Add Box collision and TextRender components. Select Box component and create OnComponentBeginOverlap event. Then select Text Render and create Toggle Visibility.