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There’s a tool in Photoshop Elements called the Smart Brush (F). This makes it quick to apply a range of photo effects, filters, adjustments and more, simply by clicking and dragging over subjects in the image that you want to apply them to.
For a selective sketched effect where some of the image remains in colour, set the tool to the Pencil Sketch option under Artistic in the Options bar. Set its Brush Size to around 25px and tick the Inverse box. Click once on the subject you want to remain in colour and two things will happen; your image will convert to a black and white sketch and a small circle selection of colour will be created where you clicked. Click within this and drag it out until the selection includes all of the subject you want to keep in colour.
The Smart Brush creates a new layer with a mask so you can use the normal Brush tool (B) on this to tidy up your selection.