Dear N;

You wrote:

1-The writer the number of whose books we did not know started speaking.

2-The writer the number of books written by whom we did not know started speaking.

3-The writer the number of whose books was not known to us started speaking.

4-The writer the number of books written by whom was unknown to us started speaking. We did not know how many books this one particular writer had written, He started speaking.

All of these sound terrible. At the very least they need commas. 2 and 4 without any punctuation make no sense at all. These are all very awkward, and no one would speak or write this way. The last unnumbered sentence is fine except for the comma splice—you need a semicolon or a period.

These are the kind of sentences that people joke about because sentences like them are sometimes found in government documents. Do  not make yourself a laughingstock, avoid such language!