You need to find the florist's husband at the beginning of Chapter 2 in A Plague Tale: Requiem to get the location of Magister Vaudin who can hopefully help Hugo.
Thankfully, you don't have too far to search, but after finding the florist's husband, you'll have to find a way inside and explore the arena to complete the chapter.
We detailed the exact location of the florist's husband in A Plague Tale: Requiem below, along with how to find a way inside the arena after you've spoke with him.
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Where to find the florist's husband in A Plague Tale: Requiem
After speaking with the florist opposite the entrance of the sheltered market stalls, she'll inform Amicia that it's actually her husband who knows Magister Vaudin's location, not her.
To find him, you'll have to locate the fountain first, which is on the other side of the sheltered stalls - but you can't cut through these stalls.
So, to find the florist's husband in A Plague Tale: Requiem, you need to turn back the way you came, then take a left towards the back stalls and you'll see him opposite the fountain with some pots and a child sitting on it. The Florist's husband is the person wearing a hat who is sweeping leaves near this fountain.
He directs you to the arena next, but when you take the the steps leading down to the arena, some guards will stop Amicia and Lucas from entering.
How to find a way inside the arena in A Plague Tale: Requiem
After getting turned away by the guards outside the arena, take a right and follow the path all the way to the animal shelter at the end, then enter it.
Opposite the donkey, on the right, you'll see a staircase. Take this to the top and interact with the door on the other side to enter the arena. You might have to wait for Lucas before you can enter the door, but this shouldn't take long.
A short loading screen and cutscene will play, then you'll get a new objective to find Vaudin, and can now explore the arena.