This particular lens has a 0.2-metre minimum focusing distance and a 20 mm maximum focal length. If you want to use a filter on the lens, then the filter size is 46 mm.
From London Camera Exchange
Panasonic Lumix G 20mm f1.7 ASPH II Black (H-H020AE-K)
Wilkinson Cameras
Panasonic Lumix G 20mm f/1.7 II Lens - Black
This product is also available at 3 unverified stores.