Query looks only for root node, because spell checker looks for suggestions by full index. So complicated query is redundant.

SQL

// make SQL query

QueryManager queryManager = workspace.getQueryManager();

// create query

String sqlStatement = "SELECT rep:spellcheck() FROM nt:base WHERE jcr:path = '/' AND SPELLCHECK('quik OR (-foo bar)')";

Query query = queryManager.createQuery(sqlStatement, Query.SQL);

// execute query and fetch result

QueryResult result = query.execute();

XPath

// make XPath query

QueryManager queryManager = workspace.getQueryManager();

// create query

String xpathStatement = "/jcr:root[rep:spellcheck('quik OR (-foo bar)')]/(rep:spellcheck())";

Query query = queryManager.createQuery(xpathStatement, Query.XPATH);

// execute query and fetch result

QueryResult result = query.execute();