Step 1
Duplicate the background layer and choose Menu: New Adjustment Layer > Hue & Saturation. Desaturate the photo (Set Saturation to -100)
Clip the Adjustment Layer to Layer 1 Keyboard - Alt(pc) / option(Mac) AND Mouse Click between the Hue Sat adjustment layer and layer 1.
Step 2
Duplicate Layer 1
Step 3
Select the newly duplicated layer (#2) and
Choose: New Adjustment Layer > Invert.
Make sure Layer 2 is selected and change the blend mode from Normal > Color Dodge. (Yes, The canvas turns white). Clip the Inverted adjustment layer to layer 2 (You'll see the down arrow in the inert adjustment layer). It will also look like the Hue & Sat layer got unclipped (that's okay)
Step 4
Make sure that Layer 2 is Selected (It's blue) If you want to adjust the sketch, you'll need to select FIRST
The Menu: Filter > Convert For Smart Filters.
Then choose Menu: Filter > Blur > Gaussian Blur...
Adjusting the amount of blur larger will make the sketch pencil strokes broader... Make a selection, click OK
Step 5
Now Save this set as a PSD file if you want to edit the sketch later.
Step 6
Flatten the layers Menu: Layers > Flatten Image. Save the Flattened image and now you now have a sketch...