Which kand of Shri Ramcharitmanas is this chaupai from?

This chaupai is from the Balakanda chapter of Shri Ramcharitmanas. This verse (chaupai) is from the Balakanda, in the context of Sitaji's worship of Gauriji. Gauriji has blessed Sitaji.

What answer does this chaupai indicate in Shri Ram Shalaka Prashnavali?

The questioner's question is excellent, the task will be accomplished.

ShriRam Shalaka

This verse (chaupai) is from the Balakanda chapter of Shri Ramcharitmanas.

Goddess Gauri blessing young Sita ji, who stands with folded hands before her temple idol in a flowering garden, her companions nearby

सुनु सिय सत्य असीस हमारी। पूजिहि मन कामना तुम्हारी॥ नारद बचन सदा सुचि साचा। सो बरु मिलिहि जाहिं मनु राचा॥

This verse (chaupai) is from the Balakanda, in the context of Sitaji's worship of Gauriji. Gauriji has blessed Sitaji.

Meaning : O Sita, listen to our true blessing, your desire will be fulfilled. Narada's word is always pure (free from doubt, delusion, etc.) and true. Whatever your heart is attached to, that blessing you will receive.

Context: where this chaupai appears in Shri Ramcharitmanas

In Balkand, after the Pushpavatika episode, Sita ji goes with her companions to the temple of Girija (Goddess Gauri). Having seen Shri Ram, her heart is already devoted to him, and she silently offers her heart's wish to the Goddess. Gauri ji herself then blesses her: listen Sita, our blessing is true; the words of Narad are always pure and true; you will attain the very groom your heart is set upon.

Transliteration

Sunu Siya Satya Asis Hamari. Pujihi Man Kamana Tumhari.. Narad Bachan Sada Suchi Sacha. So Baru Milihi Jahin Manu Racha..

Word meanings

Asis = blessing
Pujihi = will be fulfilled
Man kamana = the heart's wish
Suchi sacha = pure and true
Baru = groom, boon
Manu racha = where the mind is devotedly set

As a Shalaka answer

This blessing of Goddess Gauri is counted among the most auspicious Shalaka answers. It signals that the question comes from a good intention and that, with steady faith, the work will succeed, just as Sita ji's wish was fulfilled.