It is possible that either Shri Krishna or Arjuna told about Chakravyuha to Subhadra because Subhadra had stayed both with Arjuna and Shri Kirshna at different times during his pregnancy period and both Krishna and Arjuna knew about Chakravyuha.
But having said that, it is Abhimanyu who makes it clear from whom he learned that specific art of war. Seeing the Chakravyuha arrangement Yudhisthira says to Abhimanyu:
तवं वार्जुनॊ वा कृष्णॊ वा भिन्द्यात परद्युम्न एव वा
चक्रव्यूहं महाबाहॊ पञ्चमॊ ऽनयॊ न विद्यते [MB - 7.34.15]
Thyself, or Arjuna or Krishna, or Pradyumna, can pierce that array. O mighty-armed one, no fifth person can be found (to achieve that teat).
Then in reply Abhimanyu says:
दरॊणस्य दृढम अव्यग्रम अनीक परवरं युधि
पितॄणां जयम आकाङ्क्षन्न अवगाहे भिनद्मि च
उपदिष्टॊ हि मे पित्रा यॊगॊ ऽनीकस्य भेदने
नॊत्सहे तु विनिर्गन्तुम अहं कस्यां चिद आपदि [MB - 7.34.18,19]
Abhimanyu said, 'Desiring victory to my sires, soon shall I in battle penetrate into that firm, fierce and foremost of arrays formed by Drona. I have been taught by my father the method of (penetrating and) smiting this kind of array. I shall not be able, however, to come out if any kind of danger overtakes me
So from the words of Abhimanyu it is clear that it was Arjuna from whom he learned the secret.