Considering:

TextInput and TextEdit's openSoftwareInputPanel() and closeSoftwareInputPanel() methods have been removed. Use the new Qt.inputMethod property and call Qt.inputMethod.show() Qt.inputMethod.hide() to show and hide the virtual keyboard.
from: http://doc.qt.io/qt-5/qtquick-porting-qt5.html

Qt Code: 
  1. import QtQuick 2.3
  2. import QtQuick.Window 2.2
  3.  
  4. Window
  5. {
  6.     id:         root
  7.     visible:    true
  8.     width:      600
  9.     height:     557
  10.  
  11.     Rectangle
  12.         {
  13.             id:           numberInputBox
  14.             height:       500
  15.             width:        300
  16.             border.color: "green"
  17.  
  18.             TextInput
  19.             {
  20.                  id:             textInput
  21.                  font.pixelSize: 20
  22.                  cursorVisible:  true
  23.                  height: 500
  24.                  width: 300
  25.  
  26.                  MouseArea
  27.                  {
  28.                      anchors.fill: parent
  29.                      onClicked:
  30.                      {
  31.                          Qt.inputMethod.show()
  32.                          console.log("getPrinted")
  33.                      }
  34.                  }
  35.             }
  36.         }
  37.  
  38. }
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The text from console.log gets printed but I cannot see any keyboard on screen.