The Northern Territory, and the states of Western Australia, Queensland, New South Wales and Victoria share borders with South Australia.
Victoria has land borders with New South Wales and South Australia. It also has a sea bordwr (and a very small land/island border) with Tasmania.
South Australia
Western Australia to the West, South Australia to the South and Queensland to the East.
Tasmania has no border with South Australia.
No town in South Australia lies on the border with Victoria. The closest is probably Frances, a small township with a population of about 50, between Bordertown and Naracoorte on the now disused railway line. It is about 1 kilometre west of the border.
The state of New South Wales in Australia is bordered by Queensland on the North, South Australia on the West, and Victoria to the South.
South Australia
The question does not make sense. All of the states of Australia share a border with another state. Even Tasmania, the island state, shares an actual land border as well as a water border with another state.
There is no Australian state which shares a border with all other states. No state except for Victoria shares a land border with Tasmania. South Australia shares a border with all mainland states and the Northern Territory.
Eucla is the easternmost town of Western Australia, near the border of South Australia.
The Great Australian Bight is bordered by the two states called South Australia and Western Australia.
Victoria is bordered by New South Wales to the north and South Australia to the west. It has both a sea border and a separate land border with Tasmania.
The longest west-east border of South Australia is along its coastline. This part of the border, along the south, is 3816 km in length.