When creating a VSCode snippet, how can I transform a variable to title-case (like TitleCase)?

Try this:

  "My Snippet": {
    "scope": "typescript",
    "prefix": "snippet",
    "body": [
      "${1}() {",

      // "\treturn this.get(${TM_FILENAME_BASE/([a-z]*)-*([a-z]*)/${1:/capitalize}${2:/capitalize}/g}.FIELD.${3});",

      "\treturn this.get(${TM_FILENAME_BASE/(.*)/${1:/pascalcase}/g}.FIELD.${3});",

      "}",
      "",
      "$0"
    ],
    "description": "Creates a function wrapper for a model's attribute."
  }

EDIT : In October, 2018 the \pascalcase transform was added to vscode - see commit, but not yet added to the documentation (as of the date of this edit). I have added the much simpler transform above which accomplishes the PascalCase transform.

Demo added, uses the clipboard after the first filename case (test-bed-snippets.xxx) just to make the various possibilities easy to demonstrate.

See also snippet transform to CamelCase