Hope you great and fine.For you to get Ausbildung as a Nurse you must have good German Language both written and spoken mostly B2 for you to get a 3 years contract.
Also for you qualify for Ausbildung since you are from Nigeria which is a safe country and your asyl is rejected you must have been registered in Germany before 31 August 2015,your identity is known or you have made reasonable effort to attain your passport.
Suspension of deportation shall be granted for the duration of the vocational training specified in the training contract. Suspension of deportation pursuant to sentence 4 shall not be granted and suspension of deportation granted in accordance with sentence 4 shall expire if the foreigner has been convicted of an offence intentionally committed in the federal territory; no account shall generally be taken of fines of a total of up to 50 daily rates or of up to 90 daily rates in the case of criminal offences which can, under the Residence Act or the Asylum Act, only be committed by foreigners. If the foreigner does not undertake or discontinues the training, the training enterprise shall be obliged to notify the competent foreigners authority in writing immediately, generally within one week. The notification shall include the facts to be notified and when they arose, as well as the surnames, given names and the nationality of the foreigner. The suspension of deportation granted pursuant to sentence 4 shall expire if the foreigner no longer undertakes or discontinues the training. If the training relationship is terminated before completion or is discontinued, the foreigner shall be granted a one-time suspension of deportation for six months for the purpose of seeking another training place in order to begin vocational training in accordance with sentence 4. Suspension of deportation granted in accordance with sentence 4 shall be extended by six months for the purpose of seeking employment which is commensurate with the acquired professional qualification if, after successfully completing the vocational training for which the suspension of deportation was granted