There are still bits and pieces of the Nazcaan language in modern editions like yours. That's why every copy contains a guide to the Nazcaan alphabet. Open your Wizard's Companion and turn to the page headed "The Tools of Wizardry". If you look closely, you'll see some ancient Nazcaan script there. Your try is to try and decipher it.
To solve this puzzle, turn to page 13 of the Wizard's Companion:
Zoom on the Wizard's Robe
Translate from Nazcaan and you will get: REBIFTSENIF
But you have to read from right to left
So the answer is:
Ignore the scribbles that translate to LLEMSI (I Smell) or LLEMSJ. The actual solution is: FINEST FIBER