[RPG] What happens when a wizard tries to cast a cone of cold through a wall of fire

Applying our world's physics to a magical environment is problematic.

You are asking for two exclusive things- a RAW answer is that "the wall of force does exactly what the spell description says - no more, no less." It does no damage in any circumstance regardless of opinions on "sharpness" from that point of view.

Beyond that, you're asking for speculation, because as there is no such thing as a wall of force, it has the characteristics that you decide to apply to it. If you're running a sim game... Well, just see https://rpg.stackexchange.com/a/3461/140 for a similar "can I do X with a wall spell" analysis, as well as the other various Wall questions in the related questions sidebar. "Make it how you want, and be as physics-sim about it as you want" is the only answer.

The spell seems to be written with the idea that the huge creature would take "waves of heat" damage on the caster's turn if the creature were in range of the "waves", and "passing through" damage on the creature's turn if they moved through the wall of fire. By a simple reading, the creature would take the "waves of heat" on your turn, and "passing through damage" on the creature's turn. The same would repeat the following round if the creature was still occupying space in both the "waves" range on the caster's turn and "passing through" range on the creature's turn.

This post is similar, though dealing with a different issue.

After re-reading the spell description, it does appear the creature takes "passing through" damage on your turn (because it's "if you evoke"). With that in mind, I think the first round, the creature would take "passing through" damage on the caster's turn, and then on their turn, if they don't (or can't) get out, "passing through" again. On subsequent rounds, I would treat is as above.