Web of Science indexes all references in a paper. References to documents which are available in Web of Science are listed with links; others are marked in the reference list as [Not available]. However, it is still possible to search for these, allowing you to find all Web of Science papers that cite something even if it is not indexed.
To do a cited reference search, select Cited References on the main search page, and then enter the information you have about the source.
E.g. if we are looking for papers that cite the book Great Expectations by Dickens, we might search for Dickens C* in the 'Cited author' field, and Great Expectations 'Cited Work' field.

The next step will allow you to select the versions of the source that you are interested in. It is common for Cited References searching to have a lot of duplicates - in this case, there are 200+ because the citations are to a wide range of different editions. Tick all the ones you are interested in (the down arrow next to the tick box will let you select all results).
Finally, click See Results to get the full list of Web of Science papers citing your source, displayed as a normal search result.