I hope we agree that Guru Naanak Dev Jee asked His Guru as recorded in the referred Vaak.
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In Sikh religion the word 'Guru' has been used in three inter-related aspects:
Firstly it is used for God, the All-Pervading Divine Spirit, the Divine Light:
'The Guru is Beneficent, the Sanctuary of peace, The Guru is the Light of three worlds, He is the Eternal Being, O Nanak, he who believeth in Him, attaineth peace.' (Slok Mohalla 1, p-137) 'The Guru is All-Powerful, The Guru is the Formless Lord, The Guru is the Highest, Fathomless and Limitless, Ineffable is His praise; what can a sayer say?' (Sri Rag Mohalla 5, p-52) 'The Guru is Infinite God Himself Nanak, meditate upon such a Guru day and night.' (Asa Mohalla 5, p-387)
Secondly the word 'Guru' is also used for Guru Nanak as he was the Embodiment of God's Light:
'Guru Nanak is the perfect Guru, With the true Guru I meditateth upon God.' (Ramkali Mohalla 4, p-882) 'Guru Nanak is the true Guru, The true Guru taketh me to God.' (Kanra Mohalla 4, p-1310) 'The Guru and God are one , Divine Master pervadeth everywhere.' (Sri Rag Mohalla 5, p-53)
Thirdly the word 'Guru' is used for Gurbani, the Divine Word. Since Gurbani came direct from God, and as there is no difference between God and His order (Divine Word), Gurbani is Guru too:
'The Word is the Guru, And the Guru is the Word, The Guru's Word is full of life-giving Elixir, Whosoever shall obey, what the Word commandeth, Verily he shall get salvation.' (Nat Mohalla 4, p-982) 'The Word is the True Guru and True Guru is the Word, And the Word revealeth the path of salvation.' (Kanra Mohalla 4, p-1310)
A Gateway to Sikhism
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So its quite clear that guru nanak dev ji used word guru for god.