Bhagavad Gita · Dhyana Yoga (Atma-samyama Yoga)Chapter 6, Shloka 2 (6.2)

The shared element — giving up sankalpa.

Shankaracharya. Yaṃ sarva-karma-tat-phala-parityāga-lakṣaṇaṃ paramārtha-saṃnyāsam — the giving up of all actions and their fruits is true renunciation; yogaṃ karmānuṣṭhāna-lakṣaṇaṃ taṃ … viddhi — know yoga, which consists in performing action, to be that. The two are opposites (activity and withdrawal), so what is the similarity? Asti hi paramārtha-saṃnyāsena sādṛśyaṃ kartṛ-dvārakaṃ karma-yogasya — there is a similarity at the level of the doer: the renunciate gives up saṅkalpa, the cause of desire, and the karma yogi too karma kurvāṇa eva phala-viṣayaṃ saṃkalpaṃ saṃnyasyati — gives up the intention for the fruit while performing action. And phala-saṃkalpasya citta-vikṣepa-hetutvāt — the intention for the fruit makes the mind wander, so without giving it up no one is samādhānavān (composed). Conclusion: karma-yogasya stuty-arthaṃ saṃnyāsatvam uktam — calling karma yoga renunciation is in praise of it; and dhyāna-yogasya phala-nirapekṣaḥ karma-yogo bahiraṅgaṃ sādhanam — karma yoga that is indifferent to fruit is the outer means to dhyana yoga.

Acharya Ramanuja. Jñāna-yoga iti ātma-yāthātmya-jñānam iti prāhuḥ taṃ karma-yogam eva viddhi — what they call jnana yoga, the knowledge of the self as it truly is, know that to be karma yoga itself (knowledge is contained within karma yoga). Saṃnyasta-saṃkalpa = anātmani prakṛtau ātma-saṃkalpaḥ saṃnyastaḥ — one who has given up the notion "this is me" regarding prakriti, which is not the self. And the evidence of 4.19: yasya sarve samārambhāḥ kāma-saṃkalpa-varjitāḥ.

The difference: "Sankalpa" — Shankara: the intention for the fruit (the cause of mental distraction); Ramanuja: taking prakriti to be the self. For Shankara karma yoga is outer; for Ramanuja jnana yoga itself is contained within it.