That's a great question!
The correct unit of description is the individual claim. However, a prior-art-request should be a question about a specific patent. There is a bit of disconnect. The good news is that the claims of a patent generally relate to one another in a logical progression so lumping them into one question is fine.
At the patent application stage you are looking for prior art examples (answers to your prior-art-request) which anticipate most or all elements of the claim but ideally get at the overall idea described in the specification as well. Here is why.
Generally, the claims in a well-written patent application look like a series of nested Matryoshka dolls (apologies in advance for the over-explaining for benefit of future readers who may not have read the Shapiro article...)
The first independent claim is the biggest, broadest description of exactly what the inventor claims to have invented.
The subsequent claims ("Dependent claims") generally narrow the independent claim.
An example could be this gem from Outbrain. US Patent Application US 20130132191 A1.
The prior art request should follow the standard Ask Patents format
Claim 1 requires each and every step below:
receiving data indicating a data feed to use to create a feed-based advertisement to represent content, that is to be advertised, of a content provider;
receiving the data feed that is associated with the content to be advertised;
generating, by a server computer the feed-based advertisement using one or more data elements associated with an item in the data feed; and
providing the feed-based advertisement to a user device.
In English this means:
A method comprising
Receiving a data feed of content from a content provider who wishes to advertise its content
Creating a feed-based advertisement unit based on the data feed
Sending the feed-based advertisement to a user (presumably to display on his device)
Subsequent claims describe various narrower version of the method described in Claim 1. For example:
Claim 8 requires each and every step below:
The method of claim 1, wherein the data feed is at least one of:
a Really Simple Syndication (RSS) feed,
an atom feed
an Extensible Markup Language (XML)-based feed, or
Notice how the dependent claim expanded on specific "data feeds" which the inventor could use in the method described in the independent claim. Note that it has been a convention that "Claim 1" is the broadest claim but it is only a convention, not a rule. Another independent claim further down might be broader so all independent claims should be checked to find the broadest one.
The way we have handled this in the the standard Ask Patents prior-art-request format is to list the main independent claim (typically, Claim 1) exactly along with a plain-English version of each element of the independent claim followed by an EXTRA CREDIT section summarizing salient tweaks and limitations from the dependent claims.
By the way, users at Ask Patents don't need to get all of the elements in the claim in one single piece of prior art but when they do it's a knockout!