Having 23 Achievements with 0 missables, the full completion should take you less than an hour. As such, the walkthrough will be fairly brief but comprehensive, primarily using images of completed levels for reference, as well as a supplementary video walkthrough.
If you spot any errors or would like to advise ways to improve the walkthrough, please comment on the Walkthrough Discussion Page.
There are 10 levels total, each has two achievements associated with it: One for getting all Dogs and one for getting the Hidden Dog. I will use images of all the general dog locations then a second image of the Orchestra combination required to reveal the Hidden Dog plus its location. The images will use circles for the general Dogs and Squares for the Mystery Pieces.
If you prefer a video guide or want it as reference feel free to use this:
Huge credit to: Williams Guides on Steam for the images and help with the console changes !
Level 1 - Happy Happy Village
First load the level and immediately press 
this will reveal your cursor and unlock:
Then leave the level and press 
to unlock:
Now load in and proceed as normal.
Once you only have 1 Dog left to find, select the dogs shown below to reveal the Hidden dog in the location also shown.
All being well once you complete this level you will have unlocked:
Level 2 - Tamu-ra
Once you only have 1 Dog left to find, select the dogs shown below to reveal the Hidden dog in the location also shown.
This will unlock this levels three achievements:
Zen DogYou found the level 2 secret dog
Level 3 - Alaska
This level can be frustrating as the white of the background can make it hard to see your cursor.
Once you only have 1 Dog left to find, select the dogs shown below to reveal the Hidden dog in the location also shown.
This will unlock this levels three achievements:
Snow DogYou found the level 3 secret dog
Level 4 - Jambu Jungle
Once you only have 1 Dog left to find, select the dogs shown below to reveal the Hidden dog in the location also shown.
This will unlock this levels two achievements:
Level 5 - Orbit City
This level has one dog location different to the Windows/Steam version.
Once you only have 1 Dog left to find, select the dogs shown below to reveal the Hidden dog in the location also shown.
This will unlock this levels two achievements:
Level 6 - Earth 2805
Once you only have 1 Dog left to find, select the dogs shown below to reveal the Hidden dog in the location also shown.
This will unlock this levels three achievements:
Level 7 - Schrute Farms
The Hidden Dogs location varies to Window/Steam Version. Once you only have 1 Dog left to find, select the dogs shown below to reveal the Hidden dog in the location also shown.
This will unlock this levels two achievements:
Level 8 - Sweet Kingdom
Once you only have 1 Dog left to find, select the dogs shown below to reveal the Hidden dog in the location also shown.
This will unlock this levels two achievements:
Level 9 - Atlantis
The Hidden Dogs orchestra solution varies to Window/Steam Version. Once you only have 1 Dog left to find, select the dogs shown below to reveal the Hidden dog in the location also shown.
This will unlock this levels two achievements:
Level 10 - Life in the Mines
Once you only have 1 Dog left to find, select the dogs shown below to reveal the Hidden dog in the location also shown.
This will unlock this levels two achievements and the final two for 100% will give you the completion congrats !: