WABetaInfo reports that WhatsApp is planning to allow users to react to messages in a future update. While reactions will show up below the message, there is a separate reaction info tab that will let users see who reacted to a message.

source https://gadgets.ndtv.com/apps/news/whatsapp-message-reactions-ios-beta-info-spotted-under-development-2625372#rss-gadgets-all