I am a Ghanaian going to the Netherlands and onwards to the UK. Do Ineed a visa to enable me to continue my journey?
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