I suppose adding lyrics can't be done on the player itself. There are two types of lyrics :
1. Embedded lyrics (on ID3 tag v2, can be added through ID tag editor app on WIndows machine or Android tag editor / a few audio player apps)
2. Karaoke style lrc lyrics (could be created using app like TT player on Windows or using available app in Playstore), The "lrc" file should be named exactly the same as the related song and must be put in the same folder, Creating lrc, imho, is time consuming and inconvenient as we are forced to insert correct timestamp on the lyrics (unless it's already available somewhere, renaming is simply a single action to be taken).
Most chinese DAP, afaik, support LRC only. Since my T6 won't arrive until the end of next month, I can't confirm this as well as how to display the lyrics. I can only speculate there must be somewhere in now playing option after long-pressing particular button. Others whom are already familiar with the player should be able to explain it more accurately.
Edit:
If you are using Windows go for an app called MiniLyrics, it will integrate with Winamp. Some popular songs are available, play the songs in winamp, the lyrics will pop up automatically. You just have to save then rename exactly as your mp3 or other formats file name. In Benjie T6 case, it will show automatically on your now playing screen. But if you are into non mainstream bands you have to do the sync manually, that if you can find the lyric somewhere
