NSData* data = [session dataTaskWithRequest:request];
Incompatible pointer types initializing 'NSData' with an expression of type 'NSURLSessionDataTask'
[[_session dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
//ТУТ ВАШ КОД ДЕЛАЙТЕ С data что душе угодно.
}] resume];
// Либо так:
NSData *data = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];