For what you're likely to be seeing:
Ember Moon is the Women's Champion, having won the title after Asuka vacated it. She never beat Asuka and needs to prove herself, which seems to be setting up another multi-woman title match between her, Kairi Sane (winner of the Mae Young Classic) and Shayna Baszler (runner up in the Mae Young Classic). Either could get a singles shot though.
The Authors of Pain are a monster heel tag team who lost the titles to Sanity a few months ago. Then the Undisputed Era (Bobby Fish and Kyle O'Reilly) won the belts from Sanity. The Authors want them back, but another team called the Street Profits (they dance, they rhyme, they collect coins in cups) have said they want them too. Odds are it's the Authors vs. the Era though. The Era's stable mate Adam Cole will likely be on the card as well, possibly facing Aleister Black in a rematch from a few weeks ago.
Lars Sullivan is an unstoppable monster who will likely be fighting another unstoppable monster. Killian Dain is a candidate.
You'll also see Velveteen Dream, who is the possibly gay Prince inspired character whose feud with Aleister Black sent him flying up the charts. No word on what Black or Dream will be doing but there's almost no way they don't make the card.
Finally there's the NXT Title, with Johnny Gargano challenging Andrade Cien Almas. Andrade was a huge prospect but floundered as a face. He turned heel and got a rather gorgeous manager named Zelina Vega who got his head on straight. Almas then went on to beat Drew McIntyre to win the title in Houston in a major upset. Gargano is his first challenger and is looking to redeem himself after a horrible 2017. He lost the NXT Tag Team Titles and his partner Tommaso Ciampa turned on him (tearing his ACL in the process and putting him on the shelf for the rest of the year).
Gargano made a go of a singles run but didn't do very well, partially due to being shaken anytime he saw a shirt with himself and Ciampa on it. He kept fighting though and had some crazy good matches, including one against Pete Dunne. Then he won a mini tournament to close out the year and become #1 contender, earning the Philadelphia shot. Ciampa is rumored to be back from injury soon though, so keep an eye out for him.
I think that's everything, at least of what you're likely to see in Philadelphia.