You can copy the contents of an Architectural Desktop Layer Key Style in a "tab delimited" format that can then be pasted into any spreadsheet program that accepts tab-delimited input, such as Excel, or into a word-processing program or even Notepad. All you need to do is edit the Layer Key Style, click on the Keys tab if it is not current, right click in the list box and choose Copy All from the context menu, as shown in the image below.
Edit a layer key style by opening the Style Manager [Format > Style Manager... from the pulldown menus], then expand the Multi-Purpose Objects category and the Layer Key Style item under the drawing file that has the Layer Key Style you wish to document. In ADT 2006, select the Layer Key Style in the left pane; in ADT 2005 or 2006, right click on the Layer Key Style in the left pane and choose Edit... from the context menu. You can also open the Style Manager, filtered for Layer Key Styles, by starting the Layer Manager [the ADT Layer Manager in 2004] and clicking on the Layer Key Styles icon in the upper left corner.
Pasting into spreadsheet program is ideal, because then you can take the information and sort the rows as you like. For example, if you want to know which Layer Keys use a given color, you can sort the rows by the column with the color number. You can also do this in ADT while editing a Layer Key Style by clicking on the header at the top of a column, but this does not always work as desired [sorting on the Plotstyle column in ADT 2004 does not work well - this may have been fixed in later releases].