Exegesis:
epignous de ho Iēsous tous dialogismous auton ‘but Jesus perceiving their questionings.’ For epiginōskō cf. on 1.4; it implies thorough knowledge but does not indicate in what way this knowledge is gained. tous dialogismous autōn refers to dialogizesthai in v. 21 and hence is to be interpreted along the same lines. For dialogismos cf. on 9.46.
apokritheis ‘answering,’ cf. on 1.60.
ti dialogizesthe en tais kardiais humōn ‘what, or why, are you questioning in your hearts,’ preferably the former. Since dialogizesthe refers to discussion the addition of en tais kardiais humōn suggests that the scribes and the Pharisees do not raise objections for the sake of argument but that Jesus’ word of forgiveness is against their deepest convictions.
Translation:
Perceived their questionings, or ‘perceived that they were in discussion, or, were speaking with each other.’ Perceived, or, ‘noticed,’ ‘became aware,’ ‘observed,’ ‘came to know’ (some Indonesian languages).
Why do you question in your hearts, preferably, ‘what (matters) are you questioning in your hearts’ (cf. Exegesis). The interpretation advocated in Exegesis will require adjustments of the phrase in your hearts, leading to renderings such as, ‘what are you discussing with (all) your heart (or, so fervently)?,’ or even, ‘what are you opposing so indignantly?.’ The plural hearts is distributive, ‘(each) in/with your heart.’
The translation of vv. 21f will be different if dialogizesthai in v. 21 is rendered in accordance with interpretation (2). This may lead to a rendering of the verb “to question” by words referring to inward questioning, e.g. ‘to ponder,’ and cf. on “considered in her mind” in 1.29; of “perceived” by such words as ‘guessed’ (Sranan Tongo, lit. ‘Jesus went into their head’); and of “in your heart(s)” by ‘in your mind(s),’ ‘inwardly,’ cf. ‘why do you murmur-inside’ (Pohnpeian).
Quoted with permission from Reiling, J. and Swellengrebel, J.L. A Handbook on the Gospel of Luke. (UBS Handbook Series). New York: UBS, 1971. For this and other handbooks for translators see here . Make sure to also consult the Handbook on the Gospel of Mark for parallel or similar verses.