I'd unfold the basemesh of the sweater, then paint the pattern in photoshop, and use that as a mask in Zbrush to give a solid base across the whole mesh.
Fire up UV Master and give your model UVs, with seams where the seams would be on the shirt. Use Photoshop to make a ribbed pattern fill the UV islands going in the right direction for each piece. Apply it as the model's texture in ZBrush, go up to the highest subdiv and mask by intensity, then disable the texture and Inflate to pop out all the ribs evenly.
You should probably do the Inflate on a new Layer so you can sculpt the wrinkles/cuffs below it.
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You should probably do the Inflate on a new Layer so you can sculpt the wrinkles/cuffs below it.
edit: beaten to it
Totally forgot to add extra steps afterwards. lol -.-