There are places online that you can watch Knots Landing, although as it ended in 1993 it can sometimes be difficult to find links that still work, and the quality is not always the best.
Where to watch Knots Landing
The best site I can recommend is Watch Series. As it stands, it looks as through they have valid links for a lot of the episodes - hurrah!
The links that are "greyed" out (which appear to be from about mid-way through season 8) are the ones that when you click on them, do not have any working links for that episode.
Watch Series is a site that provides links to content, it does not actually host the content itself. This means that you have go through several different screens to actually get to the episode, and there are also a lot of pop up ads you need to navigate your way through, so be aware of that before you start.