What's the convention for describing the location of a quote on a page, without line numbers?
It is not common practice to mention the exact location of a cited item within an article. Citing the item itself would enough most of the times, and citing the page number should suffice.

If you are still concerned about citing the specific page, in the case where the content in the book is dense and heterogeneous, then you may cite them in the way @ff524 or @DanPeterson has suggested.


  p. n, mth paragraph 
  p. n, kth line


where n is the page number, m is the paragraph number, k is the line number.