My Toyota Surf 1995 - diesel engine is smoking (releasing black smoke on the exhaust). 1. Is there anything I can do to stop the problem? 2. What type of engine oil is better for the car?

First make sure your air cleaner is good and clean. Black smoke indicates lack of air and uncomplete burning of the fuel mixture. I don't like to recommend oil but you should be able to see what the manufature recomends in your manual.
any 15w/40 diesel oil is as good as another in todays world,toyota oil is one of the major oil companies anyway,if you stick to caltex esso shell ,bp any of the major oil producers you cant go wrong ,,even pensoil valvolene no worries Diesel engines require more frequent oil changes due to the carbon that escapes around the piston and rings while operating.