Let us start with the English term:

Picking (also called "order picking" or "order preparation") is defined as "taking and collecting articles in a specified quantity before shipment to satisfy customers' orders."

https://en.wikipedia.org/wiki/Order_processing

Now, let us look at the Arabic term.

I am not at all happy with the term الاختيار. This Arabic term means "picking" if by "picking" we mean "choosing." But in this context, "picking" does not really mean "choosing," as is clear from the definition above. So, why am I suggesting it to you? Simply because it is the least objectionable translation that I have found so far. The other one I found (and rejected) is السحب. The reason I rejected it is that the same term is already commonly used for the withdrawal of a product from the market for one reason or another.

The bottom line is that there is no satisfactory standard Arabic term, but الاختيار is the least objectionable one I have found.



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Note added at 33 mins (2020-05-26 16:19:36 GMT)
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I forgot to include the link to the page where I found this term:

https://ar.vayongroup.com/2246-ecommerce-shipping--handling-...

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Note added at 54 mins (2020-05-26 16:40:08 GMT)
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I am not sure I fully understand your latest question. "Picking" in this context is the activity performed in the warehouse as part of what we call "fulfillment." The workers look at the order, go to the shelf, and take the item(s) in preparation for shipping to the customer. Does this answer your question?