Angle Symbol

If you are referring to the degree symbol to represent an angle then on the keyboard tap and hold 0 (Zero) key. Angle Character or Symbol will be displayed. Else Type angle in Emoji Search option an emoji will be presented as shown in the pic below

If the above did not help then please search through the App Store in your county and you may find some, very useful. I found this paid keyboard app very interesting. ‎Special Character Keyboard on the App Store