You can use jq '.[] | .login, .id' to obtain each login followed by its id.

Do it in jq, but see @Kusalananda's answer first

jq -r '.host_components[].HostRoles.host_name | join(",")'

No, that's wrong. This is what you need:

jq -r '.host_components | map(.HostRoles.host_name) | join(",")'

Demo:

jq -r '.host_components | map(.HostRoles.host_name) | join(",")' <<DATA
{"host_components":[
  {"HostRoles":{"host_name":"one"}},
  {"HostRoles":{"host_name":"two"}},
  {"HostRoles":{"host_name":"three"}}
]}
DATA

outputs

one,two,three

You want to run a .context,.score filter on each element of v I think:

$ jq -r '.[] | [.c, .e, .score, (.v[] | .context,.score)] | @csv' file.json
"A","B",0.99,"asdf",0.98,"bcdfd",0.97

This is equivalent to using the builtin map function without assembling the results back into an array.

Here is an approach using some sample code and data from my answer to a similar question on Stack Overflow.

To choose multiple fields you can use Object Construction. E.g this filter makes an object containing just PublicDnsName and VpcId from each instance:

  .Reservations[]
| .Instances[]
| {PublicDnsName, VpcId}

If this filter is in filter.jq and the sample data from that other answer is in data.json then running

$ jq -M -f filter.jq data.json

produces

{
  "PublicDnsName": "xxxxxxxx",
  "VpcId": "vpc-eb09eb8e"
}

Once you have objects containing what you want getting the data into another format (e.g. csv) is easy. With this filter

  .Reservations[]
| .Instances[]
| {PublicDnsName, VpcId}
| [.[]]
| @csv

and the -r option

$ jq -M -r -f filter.jq data.json

jq produces

"xxxxxxxx","vpc-eb09eb8e"

To add a filtering condition, e.g. VpcId is not null, add a select.

  .Reservations[]
| .Instances[]
| {PublicDnsName, VpcId}
| select(.VpcId != null)
| [.[]]
| @csv

I recommend using String Interpolation:

jq '.users[] | "\(.first) \(.last)"'

We are piping down the result of .users[] to generate the string ".first .last" using string interpolation. \(foo) syntax is used for string interpolation in jq. So, for the above example, it becomes "Stevie Wonder" (".users[].first .users[].second" working elementwise) and "Michael Jackson".

jq reference: String interpolation