For the past two years Johnson has failed to justify his £10.5million price tag, scoring just three times each season.
Jol has overseen a transformation in Johnson's fortunes this summer, though, with the 30-year-old already finding the net three times during the club's Europa League qualifying campaign.
Jol has been impressed with Johnson and is convinced the hitman is now playing as good as he did when he tried to sign him as Tottenham manager between 2004 and 2007.
Back then Johnson was a regular in the England squad and only just missed out on a place in the 2006 World Cup squad.
Although Jol feels a return to the international fold is probably beyond Johnson, he does reckon the striker is now back to his best and he is therefore determined not to lose him when his contract expires next summer.
"When I was in England before, I was interested in signing him but he was too expensive. He was doing well at Crystal Palace and he looks the same now as he was then," Jol said.
"He's scoring goals, he's getting on the end of things, he's very good at receiving the ball.
"He is a very good second striker. He comes from midfield and he makes runs and stretches defences.
"He is doing two jobs and he is probably the only player in England who can do two jobs in one.
"He is doing very well and that's why the club are in talks with him to extend his contract."
Jol expects Johnson to sign the 12-month extension "within the next month" and is convinced the striker's well-documented injury problems are over.
"He is running like a chicken. I can't see any injuries. He is fit ," said Jol, who revealed on Friday he wants to sign up to two more players before the transfer window closes.
"I'm happy with the squad we have got, if they are fit," he said.
"That is probably not realistic though so that's why we are looking for one or two additions."
One man who Jol is convinced will feature in the England reckoning over the next 12 months is Bobby Zamora.
Zamora missed out on the 2010 World Cup thanks to an Achilles injury which he picked up after helping fire Fulham to the Europa League final.
The former Spurs striker missed a large chunk of last season after breaking his leg and he suffered yet another setback when he broke his hand last month.
Zamora has continued to play while wearing a protective cast and will do so against Aston Villa on Saturday.
Jol admits he will be key to his goal of achieving a top-half finish for the London club this term.
"The most important thing for any team is to have one or two players who can make the difference and he did that for Fulham," Jol added.
"It's not easy to find someone like him. He's a gift. He sees the ball, he can turn, he has good technique. He is a good player.
"I would like to keep him fit. Last year he had a few injury problems but this year I played him three days after (he broke his hand)."
Jol had worried that this weekend's clash at Craven Cottage - his first Premier League match in almost four years - would be called off due to the unrest in London.
With the game now being given the go-ahead, Jol is relishing his return to the English top flight after spending the summer playing Europa League qualifiers.
"We are very happy the game is on," Jol said.
"The main thing was that we wanted to play football."
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