For the osmosis docs, I see the command option:
--bounding-box top=49.5138 left=10.9351 bottom=49.3866 right=11.201
--bounding-box top=49.5138 left=10.9351 bottom=49.3866 right=11.201
for PostGIS you can use ST_MakeEnvelope(left, bottom, right, top, srid) to build a bounding box, then the &&
bounding box operator to find where the bounding boxes intersect:
SELECT *
FROM mytable
WHERE mytable.geom && ST_MakeEnvelope(10.9351, 49.3866, 11.201, 49.5138, 4326);
The SRID 4326 is for WGS84 Lat/Long, and is only required for PostGIS 1.5; it can be omitted for later versions.