The default syntax for searching the ISI Web of Knowledge is described on the "Search Rules" section of the Web of Knowledge help page.
A more complete description of specific options used for BibDesk is given on the Advanced Search page and the Advanced Search Examples page.
If you just type a search term or group of terms in the search field, BibDesk will automatically convert it to a "Topic Search" (TS=), unless you specify the field tag manually. This is an easy way of searching Title, Abstract, and Keywords, but won't work for authors.