The possessive of a noun Is the pronunciation rule of "s" the same as that of "s"?

The possessive of a noun Is the pronunciation rule of "s" the same as that of "s"?

The pronunciation rules are basically the same, when it is clear, it is clear, when it is turbid, it is turbid
But if you come across an s-ending
For example, Lewis's, lewis'at this time, just read [S]