Smells in kitchen sink
I would look at the garbage disposer.  In the bottom chamber that is connected to the drain pipe.  I would remove the drain pipe at the disposal. If possible look through the opening and see if grind up food and grease has formed a 'paste' on the inter-wall.  Fibrous vegetables can also form large gobs of waste matter after passing through the grinder.  Water is able to pass through, but the decaying waste on the wall is nearly impossible to flush out.  Unplug the disposer. Use a long thin stick, drain brush, or other items to scrape the rotten mess out of the chamber.
Reconnect the drain pipe, and flush with hot water several minutes.