Game Of Thrones: Season 6 - 8 Clues From "Battle Of The Bastards" Trailer
5. Davos Finds Out About Shireen

This looks suspiciously like Davos discovering what happened to Shireen in the lead up to Stannis' defeat by Ramsay's expedition force. He is not going to be very happy, to say the least.

So what comes next? Is he going to deal with Melisandre for putting the idea of killing the innocent girl in Stannis' head? He certainly doesn't look impressed with what he's found, and it seems likely he'll turn his anger on those responsible.
It would be legitimately great to see Davos use his stubby fingers to choke the life out of the witch-bitch, even if she's valuable to bringing people back to life. She's mostly redundant now anyway (especially with Thoros of Myr back in play) and she deserves to pay for her crimes.
Hopefully she's not going to let any more murder ghosts out of her tuppence to fight back though.
Still, as the teaser later shows, Davos sticks around to actually fight alongside Jon Snow, so this presumably is dealt with early on in the episode.

And it looks like he goes through A LOT.