Knowledge building (KB) competencies are crucial for undergraduates' creative knowledge work and academic success. While there is substantial research on KB discourse, there are limited efforts in examining how KB competencies in the conceptual, metacognitive, socio-emotional, and epistemic dimensions are demonstrated in KB discourse and how the competencies can be scaffolded. Previous studies suggest the effectiveness of reflective assessment on sustainable and productive KB discourse. This study developed a framework for analyzing KB competencies using KB discourse moves. It also examined whether a KB design augmented by reflective assessment enriched by analytic tools and artifacts could foster undergraduates' KB competencies, and if so, how. This KB design involves principle-based pedagogy with the participants engaging in collaborative inquiry and discussion on Knowledge Forum, and reflective assessment using (a) super synthesis notes, (b) KB interaction rubrics, and (c) learning analytics visualization tools. Qualitative tracking and lag sequential pattern analysis of Knowledge Forum's discourse revealed that implementing reflective assessment supported by analytics and artifacts could help the undergraduate students develop KB competencies manifested in discourse with evidence of conceptual advance, epistemic engagement, metacognition, and productive socio-emotional interactions with a collective focus. The thematic analysis illustrated the dynamics through which the design enriched by standards and visualizations helped the undergraduates develop KB competencies: leveraging synthesis super notes to promote conceptual and metacognitive advancement and epistemic engagement; employing KB interaction rubrics to cultivate metacognitive, socio-emotional, and epistemic competencies; and harnessing KBDeX visualizations to promote metacognitive and conceptual advancement and to facilitate epistemic engagement. The implications of scaffolding students' epistemic agency, metacognition, productive collaborative inquiry, and developing KB competencies in a technology-supported metacognitive learning environment are discussed.