Travis d’Arnaud has impressed the Mets this spring, but just as importantly he’s impressed himself. The biggest question concerning the 24-year-old catcher, who was the centerpiece of the R.A. Dickey trade to Toronto in December, has been answered: His left knee is again sound, after a torn posterior collateral ligament forced him to miss the second half of last season for the Blue Jays’ Triple-A team. But the performance has been there, too. “I feel like I’ve been playing really well and getting my comfort level back in the box after not playing for so long,” d’Arnaud said yesterday before going 2-for-3 in the Mets’ 3-2 exhibition victory over the Cardinals. “I’m catching well and [my] game-calling [has been good]. I feel like I’ve been doing pretty well.” D’Arnaud, who is batting .345 in 29 at-bats this spring, is still ticketed to begin the season at Triple-A Las Vegas. Barring an injury, the Mets will head north in 11 days with the catching tandem of John Buck and Anthony Recker. But there is little question within the organization that d’Arnaud will become the Mets’ starting catcher at some point this season. “He’s close — real close,” said Mets bench coach Bob Geren, the team’s catching instructor. “There are no major weaknesses.” As much as d’Arnaud’s ability has impressed Geren, the rookie’s demeanor is just as notable. Geren mentioned a mound conversation last week in which d’Arnaud was told by manager Terry Collins that Atlanta’s runner at first base, Jose Constanza, was a threat to steal. D’Arnaud broke up the meeting by telling Collins, “You know, I can throw.” Two pitches later, Constanza was thrown out by d’Arnaud.