At finally found the answer, It is very simplest one, but it takes these much time to find out,
Just added the interests
option in the following url,
NSURL* url = [NSURL URLWithString:@"http://api.linkedin.com/v1/people/~:(id,first-name,last-name,email-address,picture-url,public-profile-url,interests)"];
OAMutableURLRequest *request =
[[OAMutableURLRequest alloc] initWithURL:url
consumer:consumer
token: self.accessToken
callback:nil
signatureProvider:nil];
[request setValue:@"json" forHTTPHeaderField:@"x-li-format"];
OADataFetcher *fetcher = [[OADataFetcher alloc] init];
[fetcher fetchDataWithRequest:request
delegate:self
didFinishSelector:@selector(profileApiCallResult:didFinish:)
didFailSelector:@selector(profileCancel:didFail:)];