Knicks 7-foot-3 rookie wonder Kristaps Porzingis is back from his two-week Latvian vacation, carrying the same weight and still carrying the same burden of proving his critics wrong.

Porzingis was at the Knicks’ practice facility in Tarrytown, where about 35 rookies staged a photo shoot for their first NBA trading cards from Panini.

As usual, the 19-year-old project was in good spirits, rocking the new No. 6 jersey that he will wear this season. Porzingis wore No. 46 during the Las Vegas summer league last month because Travis Wear, a rookie last season, was being considered for training camp. But Wear won’t be invited, and Porzingis is “very happy’’ he will have the number he wore in Spain.

With coach Derek Fisher playing him at center and not his natural power-forward position, the rail-thin Porzingis drew rave reviews in Vegas for not backing down from interior physical play, blocking shots and looking poised. But the 3-point sharpshooter is not getting carried away thinking his Vegas performance means he will master his rookie season.

“I’m in between happy and my normal calm,’’ Porzingis told The Post. “I’m not thinking: ‘I did good in summer league — now I’m going to do good in the NBA.’ Our training camp will start later and I have to prove myself once again, play as hard as I can and earn my minutes. That was just summer league — a few games to see how I compare to other rookies and get a taste of American basketball.’’

Porzingis’ intense weight-gain program has barely begun. He said he still is about 232 pounds and hopes to put on at least 10 by the start of camp on Oct 1. He returned to New York on Thursday and worked out with Carmelo Anthony on Friday, both shooting and in the weight room.

“At home I was working out with my brother [Janis] a little bit, lifting weights, going to the gym, getting shots up, but I just wanted to relax a bit,’’ Porzingis said. “Once I’m here full time now, I can just concentrate on eating a lot, lifting a lot and getting stronger.’’

Porzingis wished he had more time to unwind in Europe.

“I thought I would go home and rest, but it was all interviews, media stuff,’’ he said. “A lot of interest back home, too, kind of intense. Just the last few days I went to the beach.’’

While Porzingis was away, team president Phil Jackson signed another European who played part of last season in the Spanish league, 31-year-old shooting guard Sasha Vujacic of Slovenia. Porzingis gave a thumbs up to the former Laker.

“I played against him,’’ Porzingis said. “Very experienced. He’s a cold-blooded shooter. He doesn’t care. He loves the pressure. He’s great. Those situations will help the team in those important moments. For me, it will be great having him. His experience and being European, he can teach me a lot on how hard he works. He’s a hard worker.”

At center, Porzingis, the fourth-overall pick, didn’t show off his 3-point marksmanship, launching just five treys in four games, making one.

“Maybe some 3s I received the ball and passed it back, I was kind of open,’’ Porzingis said. “It was early in the offense, I passed the ball and all the fans were, ‘Oohh, shoot it.’ I don’t want to take early shots. I could’ve popped more [on pick-and-rolls], but I rolled more times. … Once I start learning the triangle better and reading the situations better, I can get more open 3-point shots. I don’t want to force it yet.’’

But Porzingis liked the idea of trying center.

“It was something new for me,’’ he said. “I could compete with all those guys like Jahlil Okafor and see how big and strong they are. It was fun playing against them. It wasn’t easy. I think right now I’m a power forward. Once I get stronger, I can really play defense on other centers.’’

Knicks rookie point guard Jerian Grant also has worked out with Anthony. While speculation surfaced Anthony disapproved of the Porzingis pick, The Post reported he was more disappointed his buddy Tim Hardaway Jr. was traded on draft night for Grant, whom he hadn’t really seen play.

“He’s been a great, great leader — he’s the star, but at the same time one of the guys,’’ Grant said. “He’s been working out with us. He’s welcomed me with open arms.’’

Said Porzingis: “Melo’s a great guy. I’m happy to be around him.’’