Here is a list of attendance figures from the 2018/19 edition of the Champions League. Contains statistics from the group stage proper and playoff games from the Round of 16 onwards (no qualifying rounds included)
Figures updated after Final between Tottenham and Liverpool
What is the highest attendance for a Champions League game in the 2018/19 season?
Including the knockout stages, that was the 98,299 attendance for Barcelona 3-0 Liverpool (Semifinal first leg)
For the group stages, that would be the 86,290 in attendance at the Nou Camp for Barcelona vs Inter Milan on October 24, 2018. Barca, sans the injured Leo Messi, won the game 2-0.
Which is the lowest attended Champions League game in the 18/19 season?
Technically, it is the Lyon vs Shakhtar MD2 game, which was played behind closed doors, and so had an attendance of 0. That game ended in a 2-2 draw.
Otherwise, it’s the Monaco vs Club Brugge game, which saw 8,347 in attendance at Stade Louis II on November 6, 2018