וַיִּיקַ֣ץ יַעֲקֹב֮ מִשְּׁנָתוֹ֒ וַיֹּ֕אמֶר אָכֵן֙ יֵ֣שׁ יְהוָ֔ה בַּמָּק֖וֹם הַזֶּ֑ה וְאָנֹכִ֖י לֹ֥א יָדָֽעְתִּי׃
האָט יעקב זיך אױפֿגעכאַפּט פֿון זײַן שלאָף, און ער האָט געזאָגט: פֿאַר װאָר, גאָט איז פֿאַראַן אין דעם דאָזיקן אָרט, און איך האָב ניט געװוּסט.
Rashi
ואנכי לא ידעתי AND I KNEW IT NOT — for had I known it I would not have slept in such a holy place as this.
Rashbam
אכן יש ה' במקום הזה, contrary to what I thought when I lay down here that this is a totally secular place, devoid of sanctity. Every time the expression אכן occurs in Scripture it means that the person exclaiming it had to revise an opinion previously held. A well-known example is Exodus 2,14אכן נודע הדבר, when Moses made the devastating discovery that his having slain the Egyptian had not remained a secret.
Radak
'וייקץ..אכן יש ה, he concluded that this site was a site chosen for revelations, seeing that he had become the recipient of such great and wonderful visions in his dream with the ladder.