If you subscribe to the best available player (BAP) approach to the NFL Draft, then there is no position that should be ruled out of consideration when a team is on the clock. For the Jaguars though, there aren't very many positions that they could address that would be confusing and an odd position to select in the first round. Defensive tackle is one of those positions.
With Terrance Knighton and Tyson Alualu essentially locked into their starting roles with the Jaguars, a first round pick at DT would likely be a selection for a player that wouldn't have a starting role.
However, LSU DT Michael Brockers is reportedly set to visit the Jaguars before the draft according to Scout.com's Aaron Wilson. Also according to Wilson, Brockers has already visited the Panthers, Redskins and Titans, and has visits scheduled with the Rams, Browns, Buccaneers, Chiefs, Dolphins, Cowboys, Eagles, Seahawks, Patriots and Jets along with the Jaguars.
Every team selecting from picks 4-16 is listed in Wilson's report with the exception of the Bills and Cardinals so it's very possible that the Jaguars could be a team that is showing interest with the hopes that it could help put them in a position to trade down with a team interested in jumping to the top 10 to select Brockers.