Types of potato for making gnocchi
I think gnocchi should work best with varieties of potatoes that you think of as mealy, dry, and fluffy when cooked. The most common mealy potato is russet. From On Food and Cooking:


  Mealy types (russets, blue and purple varieties, Russian and banana fingerlings) concentrate more dry starch in their cells, so they're denser than waxy types. When cooked, the cells tend to swell and separate from each other, producing a fine, dry, fluffy texture that works well in fried potatoes and in baked and mashed potatoes..."


You want those that dry texture to make gnocchi, so that you can manage to wrangle it into a dough. If you live somewhere without russets, just use whatever you'd normally use for baked or mashed potatoes.

The other category of potato is waxy. They'll tend to be too solid and moist to easily make gnocchi from; they're better suited for things where you want chunks/slices to stay intact. In the US, most red, yellow, and white potatoes are waxy. Stay away from those for gnocchi.