It seems that the Carl Soderberg riddle wrapped in an enigma punctuated by a question mark might just be answered on Friday. Judging by the line pairings at Thursday’s Bruins practice at Ristuccia Arena, it would appear the 27-year-old Swedish mystery should be in the lineup when Boston suits up against the Pittsburgh Penguins for a highly anticipated, rare Friday night home game at TD Garden. He was skating alongside Chris Kelly and Jaromir Jagr on a new look third line for the Black and Gold at practice, and was chatting up fellow Europeans David Krejci and Anton Khudobin in the dressing room following practice. Claude Julien wouldn’t confirm that Soderberg will definitely suit up against the Eastern Conference’s top dog Penguins, but the Bruins are going to want to take a look at his ability level after inking him to a three-year deal last week. “He’s probable. I haven’t finalized my roster yet for [Friday], but he’s probable,” said Claude Julien. “Right now there are two new guys up front in Soderberg and [Jaromir] Jagr, and we have [Kaspars] Daugavins too. But those two guys are players that we have pegged to play on top lines hopefully, and we need to find out where they fit and what they can bring.” The 6-foot-3, 225-pound Soderberg had 31 goals and 60 points in the Swedish Elite League, and Boston’s talent evaluators have long salivated at the idea of getting the Swede’s size, skill and shooting ability into the lineup. He’s only skated for a couple of days with his B’s teammates, but he’s been placed in top-nine forward roles and has also received looks on the power play during practice sessions.