Only way I see them clearing space

The Lightning get a guy who has potential as a bottom 6 forward in Kuokkanen, and Okhotyuk is a decent D prospect since they're losing Cernak.

When it comes to New Jersey they're one of the only teams I believe actually can take on Johnson's contract without it being that big of a detriment. The team only has 3 total NHL contracts on the books after 2022, so the 4 years remaining on his deal won't be as bad.
Cernak is a great pickup for NJ as he is a standout defensive defensemen, and considering this team struggled mightily on the defensive end who can be an important building block for the future blue-line of the team.

The Lightning get a decent pick for salary relief that they desperately need.

Obviously this would come down to Killorn waiving his NTC to leave TB for LA, but he would get the opportunity to play more in LA, and be a great mentor for an up and coming team.
Cajkovic is a prospect with good goal scoring upside and Kings prospect pool could use more of those with as many playmaker as they have in their pool.