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Using jq :

$ cat json
[
  {
    "item1": "value1",
    "item2": "value2",
    "sub items": [
      {
        "subitem": "subvalue"
      }
    ]
  },
  {
    "item1": "value1_2",
    "item2": "value2_2",
    "sub items_2": [
      {
        "subitem_2": "subvalue_2"
      }
    ]
  }
]

Code:

readarray arr < <(jq '.[].item2' json)
printf '%s\n' "${arr[@]}"

Output:

value2
value2_2

Check:

Process Substitution >(command ...) or <(...) is replaced by a temporary filename. Writing or reading that file causes bytes to get piped to the command inside. Often used in combination with file redirection: cmd1 2> >(cmd2). See http://mywiki.wooledge.org/ProcessSubstitution http://mywiki.wooledge.org/BashFAQ/024

Using jq :

readarray arr < <(jq '.[].item2' json)
printf '%s\n' "${arr[@]}"

If you need a more hardened way:

readarray -td '' arr

for inputs with newlines or other special characters, avoiding word splitting.

Output:

value2
value2_2

Check:

Process Substitution >(command ...) or <(...) is replaced by a temporary filename. Writing or reading that file causes bytes to get piped to the command inside. Often used in combination with file redirection: cmd1 2> >(cmd2). See http://mywiki.wooledge.org/ProcessSubstitution http://mywiki.wooledge.org/BashFAQ/024

Using jq :

$ cat json
[
  {
    "item1": "value1",
    "item2": "value2",
    "sub items": [
      {
        "subitem": "subvalue"
      }
    ]
  },
  {
    "item1": "value1_2",
    "item2": "value2_2",
    "sub items_2": [
      {
        "subitem_2": "subvalue_2"
      }
    ]
  }
]

CODE:

arr=( $(jq -r '.[].item2' json) )
printf '%s\n' "${arr[@]}"

OUTPUT:

value2
value2_2

Using jq :

$ cat json
[
  {
    "item1": "value1",
    "item2": "value2",
    "sub items": [
      {
        "subitem": "subvalue"
      }
    ]
  },
  {
    "item1": "value1_2",
    "item2": "value2_2",
    "sub items_2": [
      {
        "subitem_2": "subvalue_2"
      }
    ]
  }
]

Code:

readarray arr < <(jq '.[].item2' json)
printf '%s\n' "${arr[@]}"

Output:

value2
value2_2

Check:

Process Substitution >(command ...) or <(...) is replaced by a temporary filename. Writing or reading that file causes bytes to get piped to the command inside. Often used in combination with file redirection: cmd1 2> >(cmd2). See http://mywiki.wooledge.org/ProcessSubstitution http://mywiki.wooledge.org/BashFAQ/024

Using jq :

$ cat json
[
  {
    "item1": "value1",
    "item2": "value2"
  },
  {
    "item1": "value1_2",
    "item2": "value2_2"
  }
]

CODE:

arr=( $(jq -r '.[].item2' json) )
printf '%s\n' "${arr[@]}"

OUTPUT:

value2
value2_2

Using jq :

$ cat json
[
  {
    "item1": "value1",
    "item2": "value2",
    "sub items": [
      {
        "subitem": "subvalue"
      }
    ]
  },
  {
    "item1": "value1_2",
    "item2": "value2_2",
    "sub items_2": [
      {
        "subitem_2": "subvalue_2"
      }
    ]
  }
]

CODE:

arr=( $(jq -r '.[].item2' json) )
printf '%s\n' "${arr[@]}"

OUTPUT:

value2
value2_2