Perhaps with some deep sea diving gear. The surface of Greenland's bedrock is close to sea level in the interior and the discovered canyon appears to in the area that is below sea level.[1]
In addition, it's estimated that a complete melting of the ice sheet would increase sea levels by ~24ft[2] and that's not taking into account the larger impact of the rest of the world melting (Antarctic ice sheet is much larger).
True, but that would need to be some kind of rebound ;).
Even ignoring sea level rises due to ice loss elsewhere and the fact that the area we're discussing already appears well below sea level, the average ratio of bedrock rise to decrease in ice shelf thickness has been running at about 1:10 in recent years.
I have no idea whether it is accurate or not but as soon as I read this I started thinking about a vastly longer version of Sam Ford Fjord and it's incredible mountain architecture:
