This research workbook operationalises the Taqrib Diagnostic–Decision Model (TDDM) as a structured instrument for studying Islamic intra-faith rapprochement. It supports the classification, diagnosis, measurement and evidence-informed analysis of Taqrib initiatives across doctrinal, social, educational, institutional, legal, cultural, digital and civilisational domains. The workbook incorporates 25 Taqrib families, 207 recognised modalities and 220 candidate indicators. It also provides a diagnostic matrix, decision tree, indicator registry, evidence register, scoring templates, validation protocols, risk register, decision ledger, action tracker and publication-readiness controls. The instrument may be used by researchers, postgraduate students, supervisors and Islamic-sects scholars to analyse historical texts, contemporary dialogue initiatives, institutional programmes and policy interventions. It is also applicable to the structured analysis of al-Murājaʿāt and comparable intra-Islamic dialogue cases. TDDM does not measure the truth, superiority or legitimacy of any Islamic school of thought. Its indicators are intended to evaluate the design, process, evidence base and practical outcomes of rapprochement initiatives. The current workbook is a research instrument and candidate operationalisation; it should not be presented as an empirically validated scale until expert validation, pilot testing and reliability assessment have been completed.