The ship you've taken your name from was indeed on the Gold Coast for the Ashantee campaign.
The first thing to note is that most
naval personnel remained aboard ship and hence didn't participate in the campaign directly. The Naval Squadron did however land a naval brigade of bluejackets and marines which took part in the land campaign with the army.
The only Navy medal roll I have the for the campaign is for those men of the Naval Brigade who were entitled to the clasp for Coomassie (ie they served with the army north of the river Prah). This roll includes 36 men of HMS Amethyst led by Lieut. Mann, but I'm afraid John Kingslake isn't on this one.
So most likely he remained aboard ship, but there's still a small chance he served ashore but didn't qualify for the clasp.
To be honest, with any naval other ranks of this period, your first plan should be to download the service record which should be easily available from TNA website http://www.nationalarchives.gov.uk/documentsonline/details-result.asp?Edoc_Id=7372351&queryType=1&resultcount=1
. I'm guessing this is him?
Lastly, here's a few images of the Ashantee campaign from the Illustrated London News
site which may interest you, the Naval Brigade wearing their distinctive sennet hats.http://www.ilnpictures.co.uk/showimage.asp?imagename=/files/ilng/images/products/76734_124442.jpghttp://www.ilnpictures.co.uk/showimage.asp?imagename=/files/ilng/images/products/76624_124342.jpghttp://www.ilnpictures.co.uk/showimage.asp?imagename=/files/ilng/images/products/76451_123708.jpghttp://www.ilnpictures.co.uk/showimage.asp?imagename=/files/ilng/images/products/76441_123698.jpg