I am a Ghanaian going to the Netherlands and onwards to the UK. Do Ineed a visa to enable me to continue my journey?
No you don’t. If you have a visa for U.K. you can go there from anywhere as long as you have all the applicable transit visas.
You should have no problem leaving the Netherlands going to the UK if you already hold a UK visa.
There is no separate document needed to exit the Netherlands.
You could still be refused entry to the UK if there was a problem with the visa such as a significant change in your circumstances after the visa was issued. This is uncommon though