You asked

Best portrait lens for the fujifilm x t10?

Here is what the site says about that.

From Fujifilm X-T10: Fujifilm X-T10: A mirrorless camera by Fujifilm with a 16.3-megapixel APS-C sensor, announced in 2015. Specs - Maker: Fujifilm - Mount: Fujifilm X - Sensor: APS-C, 23.5 x 15.6mm, crop factor 1.5 - Resolution: 16.3 megapixels - Stabilisation: none in the body; use stabilised lenses for slow shutter speeds - Announced: 2015 - Type: mirrorless camera Focal lengths on it Lenses frame like 1.5 times their focal length on full frame: 16mm ...

From Portraits: Portraits: For portraits, the lens matters far more than the camera. A cheap body with a good portrait lens beats an expensive body with a kit zoom every time.

Quoted from this site's pages.

From these pages