Each weapon has its own skill tree. Open Skills from the left menu. It is available from level 1. There is no separate NPC. Press Buy on the node you want.
The October 9 table has four branches and five nodes each. The first node is a start node with no bonus. The numbers below are the bonus shown at that token cost, not a sum of every earlier rank. Another write-up says to read the final rank on the node. If your panel disagrees, trust the panel.
| Tokens | Attack | Critical | Defense | Speed |
|---|---|---|---|---|
| Start | No bonus | No bonus | No bonus | No bonus |
| 1 | +15% attack damage | +3% critical chance | Take 5% less damage | Move 5% faster |
| 5 | +25% attack damage | +6% critical chance | Take 10% less damage | Move 10% faster |
| 9 | +40% attack damage | +10% critical chance | Take 15% less damage | Move 15% faster |
| 11 | +60% attack damage | +15% critical chance | Take 25% less damage | Move 25% faster |
The first Attack node at +15% matches the launch-week report. Fully upgraded Attack is +60% and fully upgraded Critical is +15%.
Buy Attack first when you want faster clears. Buy Critical next if the trait or weapon already leans on crits. Buy Defense when a boss is downing you. Buy Speed when positioning, not damage, is the problem.
Tokens come from leveling and from using that weapon in runs. Spending tokens on a kit you are about to replace wastes the tree.