Question for TURKISH AIRLINES

I have a D4 Visa to south Korea in which they gave me 8 months to day but my program is a year or more: I will be travelling form Lagos to Dubai and will spend two days in Dubai and from Dubai to South Korea through Easthern China Airline: Must I buy Return ticket from Lagos to Dubai? because am not returning to Lagos rather i have onward ticket to south korea with a return to Dubai in 8 months time which i may not use.

I just want to know if is a must I must Buy Return ticket to Dubai