Next to a sound asset, you should see a small button with a play icon, press that button to preview the sound. When a sound is previewing or has been previewed the button will change to a stop button. Click the stop it to leave the preview state or abort the previewing. Previewing another sound asset while another is playing will abort the oldest one.
You will find the preview button in the sound lists and in the IR asset in the Impulse audio asset field as well in the browser. In the browser, you can also start previewing by double-clicking on the asset.
Previewing sounds from the asset browser.