Sometimes you want to only view stories from a single topic on your watchlist or from the Trending tab. Simply tap the topic from the banner across the top. If you want to select more than one topic, but not all of them, you'll need to use the desktop version for now.
In this example, we are using the Forex watchlist but only looking at stories for the EURJPY currency pair. Of course, other pairs may also appear if they are in the same article as your selected topic. The first story in the screenshot is an example of that, since it covers both EURJPY and USDCAD.