Hey,
Yes you can wear leggings but make sure it does not have any big button or anything that could arise suspension. Wear a light coloured leggins.  But you can wear trousers or Salwar/Pajama as they might be more comfortable in summers. But it entirely depends on you and your comfort level.
For detailed information about the dress code of NEET,follow the link given below:
https://medicine.careers360.com/articles/neet-dress-code
Hope this helps.
Good luck.

As per NEET 2019 dress code, Salwars and trousers are suggested for women candidates..

Please ignore Tight & Dark coloured Wear..You should wear a patiala To avoid problems At the exam time.

wear slippers or sandals with low heels as shoes are not allowed in the examination hall..

Do Not wear Metallic Items or Jewellery.