Can transplanted grafts be dislodged due to shampooing 2 weeks after transplant?

It is unlikely that you will dislodge grafts at two weeks by a gentle scrub. Just be sure to use the tips of your fingers (not fingernails), and avoid anything sharp contacting the grafts.

Shampooing at 2 weeks after the procedure is alright. Do it gently with fingertips without using nails. The scabs ideally should come off by 10days post hair transplant. After this the scabs start getting firmly attached to the skin which is no good. As far as the graft dislodgement is concerned: it's unlikely at 2 weeks post hair transplant. Skin to skin closure occurs by 7-10 days over the scalp in most healthy individuals. This means the live portion of grafts is sealed inside the skin. In fue the upper part forms a dark colored scab. This scabs can be removed by 10-12 days after hair transplant. Keeping it longer will just increase downtime and may cause skin discoloration. Also when the scabs come off, hairs might be attached to it. As I often tell patients: each graft is  like a hair building machine. Dosent matter if hair comes off, the machine will build the hair again. This hair shedding will anyways happen during shedding phase of hair transplant, whether you shampoo or not. 
PS do send a picture of the 'graft' that you feel that has come off to your hair Transplant Surgeon. He/she will be  in better position to tell what's happening. 

Hi, the key here is to “gently” scrub and not use anything sharp such as fingernails.  The best method I’ve found is to use a sponge with water and baby shampoo and gently rub in a rolling motion. If you have further concerns I advise you to contact your doctor.

I generally start washing the day after the surgery to prevent scab formation, but usually by the end of the second week, even if the grafts are lost, the stem cells will generate new hairs, see my graft anchoring study below