Is it possible as a druid to wild shape into a Giant Squid and cast Air Walk on myself to allow myself to use this form above land? And if so, what would my movement speed be.
It's complicated for a druid to use the supernatural ability wild shape to assume the form of a giant squid then cast the spell air walk to move about through the air. That's because a druid can't normally cast spells while having used wild shape to assume the form of an animal. However, with enough planning and resources, this sequence is legit. I suspect, though, the druid will find it easier first to cast air walk and then to use the supernatural ability wild shape to assume the form of a giant squid.
I also suspect that the GM will likely rule that unless the druid casts the spell air breathing or employs a similar effect so that the druid in squid form can also breathe air, the druid in giant squid form will essentially have to hold its breath while on land. That is, a normal giant squid possesses the subtype aquatic yet not the special quality amphibious. However, a druid that uses wild shape to assume the form of a creature with a swim speed gains the ability to breathe water and, apparently, does not lose the ability to breathe air! This may be an oversight that the GM is quick to correct—much to many druid players' dismay—, but a druid player may argue that the ability of assumed aquatic forms to continue to breathe air is a failsafe against a druid being mind controlled into assuming forms that could otherwise kill the druid. Ask the GM.
This GM would have a druid that uses wild shape to assume the form of giant squid then that casts the spell air walk to move about outside the water use the giant squid's swim speed as the speed of the air walk effect (limited by the druid's ability to emulate that speed as per the restrictions of the supernatural ability wild shape). That is, after all, a giant squid's only—therefore normal—speed. (Compare to the Sage's ruling for D&D 3e in this answer about flying through water.) Speed is, however, a complicated concept in Pathfinder and its antecedents, so go with the GM's ruling: the fewer discussions one has about normal speed, the better.
Note: While this GM would allow the air walk spell to be used by a druid in giant squid from, I suspect many GMs would prefer the druid employ the sky swim spell for the druid's flying squid needs, that spell—unlike the air walk spell—seemingly designed with such creatures in mind. The sky swim spell's advantage is it's one spell level lower than the air walk spell, but it's disadvantage is it has 1/10 the duration of the air walk spell. (Thanks to Bobtheaverage for bringing the sky swim spell to my attention, and Oblivious Sage for pointing out the differences between the two spells' durations.).