Ex-Forest striker Holt played with the 21-year-old at Hibernian last season.
Cummings scored 23 goals in 39 appearances as Hibs won the Scottish Championship title.
Holt told BBC Radio Nottingham: "He gets in fantastic positions. Nine out of 10 times, when he gets an opportunity you'll back him to score."
Cummings has joined the Championship side on a three-year deal for an undisclosed fee and Holt expects him to transfer his talents to England's second tier..
"He's a goalscorer," Holt added. "When the ball comes in the box he comes alive.
"He has scored bagfuls. He has stuff to work on but he is only young.
"He has worked a lot more on taking the ball and bringing the team up the pitch. That's where he will get better and better. And if he can add to what he can do then he has a good career ahead of him."
"He needs to test himself again. It's a great move. That club is a sleeping giant and if he can do what I know he can do then the fans will like him.
"I knew Forest was on the radar for him. It's a club that was fantastic for me. I loved it but it needs to be pushing get to the Premier League. Bringing in players who are hungry can only be good for the club.
"He scores goals for fun. Fans will have to give him a bit of breathing space because of where he has come from, but I am sure when he does find his feet the fans will take to him."
New Nottingham Forest signing Jason Cummings is a natural goalscorer who comes alive in the penalty box, says former team-mate Grant Holt.