Full list of all 61 Gotham Knights achievements. It takes around 40-50 hours to unlock all of the achievements in the base game on Windows.
The base game contains 48 achievements, and there are 2 DLC packs containing 13 achievements.
Defeat 40 Feral Talons, 25 Gladiator Talons, and 15 Hunter Talons
Prevent 250 crimes in Gotham City
Acquire 50 Modchips via mod fusion
Defeat 30 Mob Godmothers
Craft a complete set of Legendary equipment (Suit, Melee Weapon, Ranged Weapon)
Defeat 30 Regulator Drone Masters
Defeat 10 Man-Bats in Gotham City
Reach the maximum level as any member of the Batman Family
Unlock all Knighthood Abilities for any member of the Batman Family
Defeat 30 Freaks Bulldozers
Defeat 45 Regulator Shockers
Complete Case File 08: HEAD OF THE DEMON
Defeat 45 League of Shadows Assassins and 30 Rocketeers
Complete all 16 Training Area exercises
Complete Case File 07: THE LEAGUE OF SHADOWS
Unlock all Momentum Abilities as Batgirl, Robin, Nightwing, or Red Hood
Complete Case File 06: JACOB KANE
Collect all missing pages from the mythical Historia Strigidae
Locate all Landmarks of Gotham City
Discover all the murals for Tim's Gotham City Street Art project
Retrieve every hidden Batarang in Gotham City
Complete every Batcycle time trial
Crack the case at Gotham Reservoir
Complete all Villain Case Files
Put an inmate back behind Blackgate's bars
Go to Gotham City General Hospital after visiting hours
Complete Case File 05: THE COURT OF OWLS
Unlock all four Momentum bars as Batgirl, Robin, Nightwing, or Red Hood
Complete 50 Challenges
Crash a film set and anger the director
Unearth a Villain who shouldn't be in Gotham City
Complete Case File 04: THE MASQUERADE
Successfully protect Batman's secret identity
Interrupt a presentation at the Monarch Theater
Keep your cool and survive the storm at Elliot Center
Complete Case File 03: IN THE SHADOWS
Inflict Elemental Effects on enemies 50 times
Investigate the disruption at Quartz Labs
Find all of Bruce Wayne's hidden audio recordings
Complete Case File 02: THE RABBIT HOLE
Uncover a new problem at S.T.A.R. Labs
Discover a sketchy self-help program in Gotham's streets
Complete Case File 01: BATMAN'S LAST CASE
Visit an unlikely source at Blackgate Penitentiary
Successfully stop all Premeditated Crimes in a single night
Reach Knighthood with Batgirl, Robin, Nightwing, or Red Hood
Play as Batgirl, Robin, Nightwing, and Red Hood
Unlock an Ability for the first time
Defeat 75 Supercharged criminals
Break Supercharged criminals 50 times using Elemental Effect weaknesses