You can use GREATEST and LEAST in conjunction with the SUM function:
SQL Fiddle
Oracle 11g R2 Schema Setup:
CREATE TABLE table_name ( ITEM, LOCATION, QUANTITY ) AS
SELECT 100, 'KS', -10 FROM DUAL
UNION ALL SELECT 100, 'KS', -10 FROM DUAL
UNION ALL SELECT 100, 'KS', -20 FROM DUAL
UNION ALL SELECT 100, 'KS', 10 FROM DUAL
UNION ALL SELECT 100, 'KS', 5 FROM DUAL
UNION ALL SELECT 200, 'KS', 10 FROM DUAL
UNION ALL SELECT 200, 'KS', 20 FROM DUAL
UNION ALL SELECT 200, 'KS', 5 FROM DUAL
Query 1:
SELECT item,
location,
SUM( GREATEST( quantity, 0 ) ) AS positive_quantities,
SUM( LEAST( quantity, 0 ) ) AS negative_quantities
FROM table_name
GROUP BY item, location
Results:
| ITEM | LOCATION | POSITIVE_QUANTITIES | NEGATIVE_QUANTITIES |
|------|----------|---------------------|---------------------|
| 100 | KS | 15 | -40 |
| 200 | KS | 35 | 0 |