This does the trick, including if you have more than 1 skin in your skeleton:
for (int i = 0; i < skeleton->data->skinsCount; i++) {
spSkin* skin = skeleton->data->skins[i];
spSkinEntry *entry = spSkin_getAttachments(skin);
while (entry) {
if (entry->attachment && entry->attachment->type == SP_ATTACHMENT_POINT) {
printf("%s\n", entry->attachment->name);
}
entry = entry->next;
}
}