Although, Adobe recommends using the Adobe Analytics inbuilt libraries in Adobe DTM and all these values are configured in the dedicated fields in DTM console. That being said, there are many instances where one might want to use the Custom Analytics library (Custom Requirements, Using any other Tag Manager or No Tag Manager Used, etc) and in this case, there are certain variables that one has to configure like the ones you have given in your post.
Now, enough of background and let me come to the point. Please find my responses for each of these variables inline
Harsh: This is the variable where we provide the Report Suite ID (RSID). It can take more than one RSIDs separated by comma in case of more than 1 report suites. You can get these RSIDs values from your Adobe Analytics console by navigating to the path given: Adobe Analytics --> Admin --> Report Suites
Harsh: This value depends on the tracking server on which your Adobe Analytics account is configured by Adobe folks. Please contact Adobe Client Support to get this value. This should look something like this "<VisitorNameSpaceValue>.d2.sc.omtrdc.net" for the first party implementations.
s.visitorNamespace = "INSERT-NAMESPACE-HERE"
Harsh: The value of this variable also depends on how Adobe folks have configured your company/account for Adobe Analytics. Please contact Adobe Client Support to get this value.
Harsh: This is the Visitor ID Service Config which requires VisitorAPI.js. In case you are using the Marketing Cloud Visitor ID in DTM, you don't need to configure it in your s_code (appMeasurement.js) file. In case you need to configure this, please contact Adobe Client Care to get the value.
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However, if you have a special reason for not following this best practice, and need to get those values:
s.account, s.trackingServer, s.visitorNamespace - this can come from the following location:
Adobe Analytics > Admin > Code Manager > The link at the very bottom of the page to the Legacy Code Manager >
There, you'll find:
s_account - this is your s.account, and the other two are listed as requested a little further down the JS file.