How to calculate pixel area of a clipped image in Google Earth Engine?

If the images is not masked at any pixel, it wouldn't make much sense to calculate the pixel area, since it will be the area of the geometry.

This would be an example on calculating the area of "vegetated" pixels

var s2 = ee.ImageCollection('COPERNICUS/S2')
var geometry = ee.Geometry.Polygon(
        [[[-54.706003083973854, -27.1180763669586],
          [-54.706003083973854, -27.12567743494121],
          [-54.69518841722581, -27.12567743494121],
          [-54.69518841722581, -27.1180763669586]]], null, false)

var col = s2.filterBounds(geometry).limit(10)
var ndvi = col.map(function(img){ return img.normalizedDifference(['B8', 'B4']).rename('ndvi')})
var mosaic = ndvi.mean().clip(geometry)

var veg_thres = 0.5

var area_image = ee.Image.pixelArea().divide(1e4)
var final = mosaic.addBands(area_image)
var masked = final.updateMask(mosaic.gte(veg_thres))

Map.addLayer(masked, {bands:['ndvi'], palette:['yellow', 'green']}, 'NDVI')

var vegetated_area = masked.select('area').reduceRegion(
  {
    reducer: ee.Reducer.sum(),
    geometry: geometry,
    scale: 10
  }
)

var total_area = final.select('area').reduceRegion(
  {
    reducer: ee.Reducer.sum(),
    geometry: geometry,
    scale: 10
  }
)

print('vegetated area (ha):', vegetated_area.get('area'))
print('total area (ha):', total_area.get('area'))

link: https://code.earthengine.google.com/e134cd8a50e68bcbb20e877ee1434fc0