How i can find the sales-force Marketing cloud sub-domain ? I was trying to use the sub domain for API call purposes but i am not able to find the sub-domain.
Do you mean the endpoints? https://developer.salesforce.com/docs/atlas.en-us.noversion.mc-apis.meta/mc-apis/wsdl-endpoint-links.htm
The Salesforce documentation is a good place to start before you post questions on stack exchange.
The SubDomain you are referring to are automatically generated when you create an Installed Package. Administration > Account > Installed Package
Use this doc to help locate your TSE:
TL;DR when you create an installed package to get clientid/secert it provides your subdomain