This is an example of how to specify an ipAddress when making a getOffers method call. Simply add it to the geo object of the request context.

target-nodejs-sdk-ipaddress-demo.js

const TargetClient = require("@adobe/target-nodejs-sdk");

const client = TargetClient.create({
  client: "adobesummit2018",
  organizationId: "65453EA95A70434F0A495D34@AdobeOrg"
});

client
  .getOffers({
    request: {
      context: {
        channel: "web",
        geo: {
          ipAddress: "79.14.121.7"
        }
      },
      execute: {
        mboxes: [{ name: "demo-marketing-offer1" }]
      }
    }
  })
  .then(result => {
    console.log(result);
  });