do I need alchemy skills to make that potion myself?
No you don't.
<span class='standouttext'>Spoiler : </span><span class='spoiler'>
In the alchemist house you have some "special potions", two yellow and two purple. Mix the first yellow with first purple. They will disappear (nothing to worry about). Mix the second yellow with the second purple, and the needed potion will appear.
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