Practicum in Advanced Alchemy is a Skellige side quest with suggested level 24.

You can pick this quest up from Gremist in Geydneith. It involves helping Gremist with three tasks to perform a ritual, and then he will teach Geralt what he knows of alchemy.

Find Fritjof the druid in the nearby village and convince him to talk help Gremist with the ritual. Fritjof will ask for help to perform a rain summoning ritual, and then he will go see Gremist.Once Fritjof starts the ritual, you will encounter many Foglet enemies.

Find pimpernel in the woods using witcher senses. Once at the supposed location of the pimpernel, Geralt will encounter someone saying various druids have come searching for and failed to find the pimpernel. Use witcher senses and follow the footprints leading away. Some wolves, as well as an arachas may appear and attack, so deal with them, then continue following the footprints. You will eventually find the missing druid, Ramund, as well as a "horny goat woman".

You can decide to kill her, or let her go. If you kill her, you can get your hands on the rare Succubus Mutagen, needed for the Succubus Decoction. If you spare her, you get peace of mind that you're not an evil man.

Follow the path she took, to find her lair, and where you can find the pimpernel.

Head towards the abandoned distillery. You will need to deal with some Alghouls near the distillery entrance. Once inside, there is also a Cyclops inside that must be killed. After dealing with the cyclops, look around using witcher senses to try and find the instructions on how to produce the alcohol. After you find the Distiller's Letter, read it. The first step will be to find some mash, which will be up the ladder. Get the mash, and put it in the evaporator, and then light the fire under the evaporator using Igni. Then cool the condenser, then turn the river lever then the left lever. Then collect the alcohol in the nearby barrel.

Head back to Gremist to give him the ingredients. Meditate/rest for one day, then return. Talk to Gremist again to complete the quest.