How do i breed hymogonoy tobiana for game ?

Get a Mare that is ToTo and breed to a Stallion that is ToTo

Does that mean that both parents simply need to have ToTo in their gene testing? How do you know they are toto dominant?

You can tell from the pattern, some of the time. It can be obscured by other patterns. Alternately, you can look at the genetic test.

If both parents are ToTo, they are homozygous tobiano, and will guarantee a ToTo foal.

If the horse is Toto, they are heterozygous tobiano, and will pass along the tobiano gene to 50% of their foals. If bred to a ToTo horse, they will produce a ToTo foal 50% of the time.

If the horse is toto, it does not carry the tobiano gene. It cannot produce a ToTo foal.