Can I display the percentage of scaling during zoom in or zoom up

take slider widget in your 2D canvas. here you can see the properties of slider widget.

you can these properties like initial value 0 , maximum 360(u can take according your need ) and intervals you can decide like step.

you can refer below link for reference.

http://support.ptc.com/help/vuforia/studio/en/index.html#page/Studio_Help_Center%2FBeginner_Bindings.html%23

bind the value property with model by selecting SCALE factor from list.

then create application parameter of name scale.

now bind the value property to application parameter scale 

now bind scale application parameter with label widget as shown in figure 

so in preview label widget reflect the scaling value.