Assume that: 1. the original text lacks line numbers
- and counting the line numbers (for each citation) is too inefficient, for both you and the reader.
Is it conventional to write the beneath?
This quotation is from p. 10 ( [one of:] Top, Middle, Bottom).
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.