How do i get letter " ž " on my keyboard?

What country are you in and therefore which keyboard layout are you using ? If you press and hold the 'z' or 'd' keys, then after a second or so you might (it depends upon the keyboard layout that you've chosen) get a popup with alternatives for those letters, and you can then slide your finger up to select an alternative, and then release the screen to type it. Here in the UK with an 'English (UK)' keyboard I get the 'ž' as an option on the 'z' key - ž and đ appear on the 'Serbian (latin)' keyboard as options on the z and d keys respectively, not sure about other layouts.