Is it possible to install the .snap application in an offline computer?

It seems you first have to download and install the ubuntu-core snap before you can do offline installs for any other snaps. For me this worked:

Run the following commands on an online Ubuntu system:

snap download ubuntu-core
snap download somePackage

This will put the following files in your current directory:

ubuntu-core_1797.assert
ubuntu-core_1797.snap
somePackage.assert
somePackage.snap

Copy these files to the offline system, then install them (from the directory they were copied to):

sudo snap ack ubuntu-core_1797.assert
sudo snap install ubuntu-core_1797.snap
sudo snap ack somePackage.assert
sudo snap install somePackage.snap

This should solve the problem @lane had where it tried to connect to the internet while installing a local .snap file.

First of all, you can indeed install debs offline:

$ sudo dpkg -i <deb>

However, you're right in that it doesn't take into account the deb's dependencies-- you actually need to have the deb and all its dependencies available offline in order to successfully install it:

$ sudo dpkg -i <deb> <dependency1> <dependency2> ...

So yes, installing a snap offline is very easy, and all you need to have is that single snap (since as you know, it includes its dependencies):

$ sudo snap install path/to/snap