A level 6 field node in Doomsday: Last Survivors is basically a high-tier world resource node, and the usual way to get one is to look farther from your base or closer to stronger map areas, since higher-level nodes tend to appear in better zones and near the metropolis. Reports from players also say world resource nodes respawn indefinitely after being emptied, so you usually need to keep scouting rather than relocating endlessly.

What players say works

  • Search farther out on the map; higher-level nodes are more common near the metropolis.
  • Use the resource map filter so you only see resource nodes and can spot the higher ones faster.
  • Keep gathering and checking the same regions, because nodes respawn after depletion.

Important distinction

Some players use “field node” to mean a world gathering node, while others mean alliance territory resources. Alliance resource nodes are different: they are captured through alliance territory and show a red flag instead of a normal node level.

If you mean tier 6 progression

If you were actually asking about unlocking T6 troops, that is a much bigger upgrade path and requires major building and research progress, including level 25 core buildings and maxing the relevant research trees.

Best practical move

The fastest route is usually to scout the map, filter for resources, and gather in stronger zones until level 6 nodes appear near your alliance’s territory or around the metropolis.

TL;DR: level 6 resource nodes are usually found by scouting better map zones, especially farther out or near the metropolis, and they respawn after being harvested.