Summary

String sqlQuery = "SELECT [This],* FROM [Folder] WHERE ([This] INSUBFOLDER '+ path + "') AND ([FolderName] = '" + refNo + "')";
SearchSQL sql = new SearchSQL(sqlQuery);
SearchScope scope = new SearchScope(objectStore);
IndependentObjectSet set = scope.fetchObjects(sql, null, null,false);

Example use NoLock
SELECT * FROM Person.Contact WITH (NOLOCK) WHERE ContactID < 20
If we would like to use Filenet API (Java) to query in ICN Plugin Service..." How can we apply NOLOCK in api query on above?

There is no NOLOCK option in the Content Platform Engine(CPE) SQL syntax, but there is also no need for any such option.
The CPE API is completely stateless.  Each command completes, and commits it's transaction before returning to the caller.  So SQL DB resources are never left in a locked state after a call to the Content Engine(CE) API. 
Additionally, the CE SQL syntax is read only (no INSERT/UPDATE/DELETE) so there is not a transaction in the first place for CE API queries.  They are read only queries that don't take locks.