From Wiktionary, the free dictionary
ن٘ • (ṅ)
- medial form of ں (ṉ)
- Marks the medial nasalization in Nastaliq, with the character ن (nūn) marked with the maghnūna diacritic: respectively ں (̃) - the final form.
This is not a letter per se, rather a combination of ن (n) + ◌٘ (“ghunnah mark”) and is rarely used, mostly to clear ambiguity.