Here is the full list of all 38 It's Quiz Time achievements.
Complete a game with 8 players
A new player wins the game
Someone joins mid-game
The same player answers every question incorrectly during All in Order
Play on October 31st
The same player works alone against a team of two or more players in Showdown 5 times
Finish a Solo Score Attack game with zero points
Complete 10 games with friends
The same player is leading at the end of every round and wins the game
A player scores over 9,999 points in a multiplayer game
The same player answers every question correctly during All in Order
The leader beats a team of two or more players in Showdown
A player goes from last place after the first round to winning the game
Complete a game with friends
A player correctly answers all specialist subject questions during The Big Finish
A player scores over 450 points on a single question in The Big Finish
A team of two or more players beats the leader in Showdown
Complete a Solo Score Attack game
Complete 30 games with friends
Play two back-to-back games with the same players
The same player wins three games in a row
All players answer every question correctly during the Starter Round
No-one answers incorrectly during a round of Connections
A player guesses only one clue during Describe It!
A player correctly guesses every clue for a subject in Describe It!
Someone calls 'Shenanigans!' during Describe It!
A clue is removed during Describe It! after someone calls 'Shenanigans!'
A player answers correctly during Trust or Bust when all other players predicted otherwise
No-one answers correctly during Trust or Bust
The same player correctly predicts that everyone will answer correctly during Trust or Bust
The same player predicts everyone will answer incorrectly during Trust or Bust
Everyone answers correctly in Best Friends Forever, apart from the best friend
Best friend fails to correctly predict player's answer in Best Friends Forever
The same player is chosen as the best friend by all players in a round of Best Friends Forever
All players choose the same specialist subject during The Big Finish
All players in a 4-player multiplayer game finish with over 7,500 points
Score over 8,000 points in the Solo Score Attack
Play on December 25th