If you mean the tools palette then the visibility is toggled with the Tab key.
If you mean the Tool options dialog:
- Click the
◁
icon on the right of the tab line where the Tool options usually appears

- Select
Add tab ➤ Tool options
- You can drag the added tab index over the first tab index in the line to move the Tool options tab to the first position.
- You can avoid losing the Tool options dialog by locking it in place, after adding it, click the
◁
icon again and select Lock tab to dock
.
For more details and screen shots see here
Otherwise if all else fails, you can reset to factory settings like this (reinstall doesn't reset settings...): Edit > Preferences > Interface > Window management > Window positions > Reset saved windows Positions to Defaults values

See here for some hints about managing your window positions.